1. Ligaments, mesenteries and bursae of perіtoneum in adults
2. Practical skills on digestive system
3. Respiratory organs. Structure and function of nose
Lesson No 14
Theme 1. Ligaments, mesenteries and bursae of perіtoneum in adults
Transition of parietal peritoneum into visceral peritoneum realizes by derivatives: ligament, mesentery and omentum. If organ covered by peritoneum from all sides, such position is called intraperitoneal; if from three sides - mesoperitoneal position; if only one side - extraperitoneal or retroperitoneal.
Abdominal cavity is limited:
· above - by diaphragm
· anteriorly and laterally - by muscles, fasciae, skin
· behind - by lumbar and sacral portions of backbone and lumbar muscles
· from below – by bones, ligaments and muscles of pelvis.
Abdominal cavity contains the organs of digestive and urogenital systems and spleen.
Front view of the thoracic and abdominal viscera. a. Median plane. b b. Lateral planes. c c. Trans tubercular plane.
d d. Subcostal plane. e e. Transpyloric plane
Regions.—For convenience of description of
the viscera, as well as of reference to the morbid conditions of the contained
parts, the abdomen is artificially divided into nine regions by imaginary
planes, two horizontal and two sagittal, passing through the cavity, the edges
of the planes being indicated by lines drawn on the surface of the body. Of the
horizontal planes the upper or transpyloric is indicated by a line
encircling the body at the level of a point midway between the jugular notch
and the symphysis pubis, the lower by a line carried around the trunk at the
level of a point midway between the transpyloric and the symphysis pubis. The
latter is practically the intertubercular plane of Cunningham, who
pointed out 163 that its level corresponds with the prominent and easily defined
tubercle on the iliac crest about
The middle region of the upper zone is called the epigastric; and the two lateral regions, the right and left hypochondriac. The central region of the middle zone is the umbilical; and the two lateral regions, the right and left lumbar. The middle region of the lower zone is the hypogastric or pubic region; and the lateral regions are the right and left iliac or inguinal.
The pelvis is that portion of the abdominal cavity which lies below and behind a plane passing through the promontory of the sacrum, lineæ terminales of the hip bones, and the pubic crests. It is bounded behind by the sacrum, coccyx, Piriformes, and the sacrospinous and sacrotuberous ligaments; in front and laterally by the pubes and ischia and Obturatores interni; above it communicates with the abdomen proper; below it is closed by the Levatores ani and Coccygei and the urogenital diaphragm. The pelvis contains the urinary bladder, the sigmoid colon and rectum, a few coils of the small intestine, and some of the generative organs.
When the anterior abdominal wall is removed, the viscera are partly exposed as follows: above and to the right side is the liver, situated chiefly under the shelter of the right ribs and their cartilages, but extending across the middle line and reaching for some distance below the level of the xiphoid process. To the left of the liver is the stomach, from the lower border of which an apron-like fold of peritoneum, the greater omentum, descends for a varying distance, and obscures, to a greater or lesser extent, the other viscera. Below it, however, some of the coils of the small intestine can generally be seen, while in the right and left iliac regions respectively the cecum and the iliac colon are partly exposed. The bladder occupies the anterior part of the pelvis, and, if distended, will project above the symphysis pubis; the rectum lies in the concavity of the sacrum, but is usually obscured by the coils of the small intestine. The sigmoid colon lies between the rectum and the bladder.
When the stomach is followed from left to right it is seen
to be continuous with the first part of the small intestine, or duodenum, the
point of continuity being marked by a thickened ring which indicates the
position of the pyloric valve. The duodenum passes toward the under surface of
the liver, and then, curving downward, is lost to sight. If, however, the
greater omentum be thrown upward over the chest, the inferior part of the
duodenum will be observed passing across the vertebral column toward the left
side, where it becomes continuous with the coils of the jejunum and ileum.
These measure some
The spleen lies behind the stomach in the left hypochondriac region, and may be in part exposed by pulling the stomach over toward the right side.
The glistening appearance of the deep surface of the abdominal wall and of the surfaces of the exposed viscera is due to the fact that the former is lined, and the latter are more or less completely covered, by a serous membrane, the peritoneum.
the Peritoneum (Tunica Serosa)—The peritoneum is the largest serous membrane in the body, and consists, in the male, of a closed sac, a part of which is applied against the abdominal parietes, while the remainder is reflected over the contained viscera. In the female the peritoneum is not a closed sac, since the free ends of the uterine tubes open directly into the peritoneal cavity. The part which lines the parietes is named the parietal portion of the peritoneum; that which is reflected over the contained viscera constitutes the visceral portion of the peritoneum. The free surface of the membrane is smooth, covered by a layer of flattened mesothelium, and lubricated by a small quantity of serous fluid. Hence the viscera can glide freely against the wall of the cavity or upon one another with the least possible amount of friction. The attached surface is rough, being connected to the viscera and inner surface of the parietes by means of areolar tissue, termed the subserous areolar tissue. The parietal portion is loosely connected with the fascial lining of the abdomen and pelvis, but is more closely adherent to the under surface of the diaphragm, and also in the middle line of the abdomen.
The space between the parietal and visceral layers of the peritoneum is named the peritoneal cavity; but under normal conditions this cavity is merely a potential one, since the parietal and visceral layers are in contact. The peritoneal cavity gives off a large diverticulum, the omental bursa, which is situated behind the stomach and adjoining structures; the neck of communication between the cavity and the bursa is termed the epiploic foramen (foramen of Winslow). Formerly the main portion of the cavity was described as the greater, and the omental bursa as the lesser sac.
The peritoneum differs from the other serous membranes of the body in presenting a much more complex arrangement, and one that can be clearly understood only by following the changes which take place in the digestive tube during its development.
To trace the membrane from one viscus to another, and from the viscera to the parietes, it is necessary to follow its continuity in the vertical and horizontal directions, and it will be found simpler to describe the main portion of the cavity and the omental bursa separately.
Vertical Disposition of the Main Peritoneal Cavity (greater sac)—It is convenient to trace this from the back of the abdominal wall at
the level of the umbilicus. On following the peritoneum upward from this level
it is seen to be reflected around a fibrous cord, the ligamentum teres (obliterated
umbilical vein), which reaches from the umbilicus to the under surface of
the liver. This reflection forms a somewhat triangular fold, the falciform
ligament of the liver, attaching the upper and anterior surfaces of the
liver to the diaphragm and abdominal wall. With the exception of the line of
attachment of this ligament the peritoneum covers the whole of the under
surface of the anterior part of the diaphragm, and is continued from it on to
the upper surface of the right lobe of the liver as the superior layer of
the coronary ligament, and on to the upper surface of the left lobe as the superior
layer of the left triangular ligament of the liver. Covering the upper and
anterior surfaces of the liver, it is continued around its sharp margin on to
the under surface, where it presents the following relations: (a) It
covers the under surface of the right lobe and is reflected from the back part
of this on to the right suprarenal gland and upper extremity of the right
kidney, forming in this situation the inferior layer of the coronary
ligament; a special fold, the hepatorenal ligament, is frequently
present between the inferior surface of the liver and the front of the kidney.
From the kidney it is carried downward to the duodenum and right colic flexure
and medialward in front of the inferior vena cava, where it is continuous with
the posterior wall of the omental bursa. Between the two layers of the coronary
ligament there is a large triangular surface of the liver devoid of peritoneal
covering; this is named the bare area of the liver, and is attached to
the diaphragm by areolar tissue. Toward the right margin of the liver the two
layers of the coronary ligament gradually approach each other, and ultimately
fuse to form a small triangular fold connecting the right lobe of the liver to
the diaphragm, and named the right triangular ligament of the liver. The
apex of the triangular bare area corresponds with the point of meeting of the
two layers of the coronary ligament, its base with the fossa for the inferior
vena cava. (b) It covers the lower surface of the quadrate lobe, the
under and lateral surfaces of the gall-bladder, and the under surface and
posterior border of the left lobe; it is then reflected from the upper surface
of the left lobe to the diaphragm as the inferior layer of the left
triangular ligament, and from the porta of the liver and the fossa for the
ductus venosus to the lesser curvature of the stomach and the first
It encircles the intestine, and subsequently may be traced, as the posterior layer of the mesentery, upward and backward to the abdominal wall. From this it sweeps down over the aorta into the pelvis, where it invests the sigmoid colon, its reduplication forming the sigmoid mesocolon. Leaving first the sides and then the front of the rectum, it is reflected on to the seminal vesicles and fundus of the urinary bladder and, after covering the upper surface of that viscus, is carried along the medial and lateral umbilical ligaments on to the back of the abdominal wall to the level from which a start was made.
Peritoneal cavity is complex of fissure between abdominal organs and walls lined by parietal and visceral sheets that contain serous liquid. It can be subdivided into superior storey and inferior storey, also cavity of lesser pelvis.
Superior storey of peritoneal cavity positioned between diaphragm and level of mesocolon of transverse colon. It contains:
• hepatic bursa surrounds right hepatic lobe and gallbladder;
• pregastric bursa accommodates left hepatic lobe and anterior wall of stomach;
• omental bursa is situated behind lesser omentum and it is in touch with posterior stomach surface.
Lesser omentum is formed by double peritoneal sheet that forms of hepatogastric ligament and hepatoduodenal ligament. Lesser omentum carries common bile duct, portal vein and proper hepatic artery (DVA).
Vertical disposition of the peritoneum. Main cavity, red; omental bursa, blue
Hepatic bursa communicates with omental bursa by the medium of epiploic foramen (of Winslow). Last limited from above by caudate lobe of the liver, from below - by superior part of duodenum, anteriorly - hepatoduodenal ligament, behind - by parietal sheet of peritoneum.
Greater omentum develops from 4 peritoneal sheets, which continue from gastrocolic ligament and, freely hanging down, covers the abdominal organs in front. The gastrocolic ligament connects the transverse colon with the greater curvature of the stomach.
Inferior floor of peritoneal cavity extends from mesocolon of transverse colon to entrance into lesser pelvis.
Root of small intestine mesentery divides the inferior storey into right and left mesenteric sinuses. They accommodate the loops of small intestine. Right mesenteric sinus is bordered by mesenteric root and ascending colon. In place, where ileum continues into cecum superior and inferior ileocecal recesses are situated. One can see retrocecal recess behind cecum. Right paracolic sulcus runs between ascending colon and parietal peritoneum of lateral abdominal wall. Mesenteric root, descending colon and sigmoid colon border left mesenteric sinus. Superior and inferior duodenal recesses are positioned in area of duodenojejunal junction. Mesocolon of sigmoid forms intersigmoidal recess. Left paracolic sulcus runs between descending colon and parietal peritoneum of left abdominal wall.
Parietal sheet of peritoneum covering back surface of anterior abdominal form plicae (folds) and fossae. The median umbilical fold contains the remnant of the embryonic urachus; the medial umbilical folds carry obliterated umbililal arteries; lateral umbilical folds contain inferior epigastric arteries. Supravesical fossae positioned between median and medial umbilical folds. Medial umbilical fossae located between medial and lateral umbilical folds. Lateral umbilical fossae located laterally from lateral umbilical folds. Medial and lateral umbilical fossae can be projected into superficial inguinal ring and deep inguinal ring.
Posterior view of the anterior abdominal wall in its lower half. The peritoneum is in place, and the various cords are shining through
Cavity of lesser pelvis
Peritoneal cavity in the male pelvis contains rectovesical excavation (pouch). Peritoneum in the female between uterus and urinary bladder form vesicouterinae excavation. Behind the uterus peritoneum descends into the rectouterine pouch (pouch of Douglas), which is the lowest point of the peritoneal cavity. That is why some liquid from all peritoneal cavity can collect here during some pathology. The entrance into the rectouterine pouch is narrowed by the rectouterine folds, in which the rectouterine muscles run.
Theme 2. Practical skills on digestive organs preparations
1, 11th rib.
2, Vertebral body (TH 12).
3, Gas in stomach.
4, Gas in colon (splenic flexure).
5, Gas in transverse colon.
6, Gas in sigmoid.
7, Sacrum.
8, Sacroiliac joint.
9, Femoral head.
10, Gas in cecum
11, Iliac crest.
12, Gas in colon (hepatic flexure).
13, Psoas margin.
1, Liver. 2, Gallbladder. 3, Stomach. 4, Transverse colon. 5, Small Intestine. 6, Sigmoid. 7, Cecum.
Entero-MRI, coronal section, T2-weighted. Image 11
1, Liver. 2, Gallbladder. 3, Hepatic (or the right colic) flexure. 4, Wing of ilium (or ala). 5, Cecum. 6, Urinary bladder. 7, Sigmoid. 8, Small Intestine. 9, Superior mesenteric vein. 10, Splenic vein. 11, Descending colon. 12, Splenic (or left colic) flexure. 13, Stomach.
Entero-MRI, coronal section, T2-weighted. Image 15
1, Liver. 2, Portal vein. 3, Hepatic (or the right colic) flexure. 4, Ascending colon. 5, Inferior vena cava. 6, Abdominal aorta. 7, Right common iliac artery. 8, Left common iliac artery. 9, Small Intestine. 10, Urinary bladder. 11, Sigmoid 12, Colon. 13, Descending colon. 14, Spleen. 15, Stomach.
Entero-MRI, coronal section, T2-weighted. Image 25
1, Liver. 2, Right kidney. 3, Ascending colon. 4, Uterus. 5, spinal canal (or vertebral). 6, Small Intestine. 7, Descending colon. 8, Left kidney. 9, Spleen.
Sagittal reconstruction Image 40
1, Vertebral body (thoracic spine). 2, Spinous process. 3, Aorta. 4, Vertebral body (lumbar spine, L1). 5, Intervertebral disc. 6, Sacrum. 7, Rectum. 8, Bladder. 9, Small bowel. 10, Hepatic vein. 11, Liver. 12, Heart.
Sagittal reconstruction Image 37
1, Aorta. 2, Psoas muscle. 3, Iliac artery. 4, Bladder. 5, Liver. 6, Heart.
Theme3. Respiratory organs. Structure and function of nose
The respiratory apparatus consists of the nose, nasal cavity, larynx, trachea, bronchi, lungs, and pleuræ.
The head and neck of a human embryo thirty-two days old, seen from the ventral surface. The floor of the mouth and pharynx have been removed
Development.—The rudiment of the respiratory organs appears as a median longitudinal groove in the ventral wall of the pharynx. The groove deepens and its lips fuse to form a septum which grows from below upward and converts the groove into a tube, the laryngo-tracheal tube, the cephalic end of which opens into the pharynx by a slit-like aperture formed by the persistent anterior part of the groove. The tube is lined by entoderm from which the epithelial lining of the respiratory tract is developed. The cephalic part of the tube becomes the larynx, and its next succeeding part the trachea, while from its caudal end two lateral outgrowths, the right and left lung buds, arise, and from them the bronchi and lungs are developed. The first rudiment of the larynx consists of two arytenoid swellings, which appear, one on either side of the cephalic end of the laryngo-tracheal groove, and are continuous in front of the groove with a transverse ridge (furcula of His) which lies between the ventral ends of the third branchial arches and from which the epiglottis is subsequently developed. After the separation of the trachea from the esophagus the arytenoid swellings come into contact with one another and with the back of the epiglottis, and the entrance to the larynx assumes the form of a T-shaped cleft, the margins of the cleft adhere to one another and the laryngeal entrance is for a time occluded. The mesodermal wall of the tube becomes condensed to form the cartilages of the larynx and trachea. The arytenoid swellings are differentiated into the arytenoid and corniculate cartilages, and the folds joining them to the epiglottis form the aryepiglottic folds in which the cuneiform cartilages are developed as derivatives of the epiglottis. The thyroid cartilage appears as two lateral plates, each chondrified from two centers and united in the mid-ventral line by membrane in which an additional center of chondrification develops. The cricoid cartilage arises from two cartilaginous centers, which soon unite ventrally and gradually extend and ultimately fuse on the dorsal aspect of the tube.
J. Ernest Frazer has made an important investigation on the development of the larynx and the following are his main conclusions:
The opening of the pulmonary diverticulum lies between the two fifth arch masses and behind a “central mass” in the middle line—the proximal end of the diverticulum is compressed between the fifth arch masses. The fifth arch is joined by the fourth to form a “lateral mass” on each side of the opening, and these “lateral masses” grow forward and overlap the central mass and so form a secondary transverse cavity, which is really a part of the cavity of the pharynx. The two parts of the cavity of the larynx are separated in the adult by a line drawn back along the vocal fold and then upward along the border of the arytenoid eminence to the interarytenoid notch. The arytenoid and cricoid are developed in the fifth arch mass. The thyroid is primarily a fourth arch derivative, and if it has a fifth arch element this is a later addition. The epiglottis is derived from the “central mass,” and has a third arch element in its oral and upper aspect; the arch value of the “central mass” is doubtful.
Lungs of a human embryo more advanced in development.
The right and left lung buds grow out behind the ducts of Cuvier, and are at first symmetrical, but their ends soon become lobulated, three lobules appearing on the right, and two on the left; these subdivisions are the early indications of the corresponding lobes of the lungs. The buds undergo further subdivision and ramification, and ultimately end in minute expanded extremities—the infundibula of the lung. After the sixth month the air-sacs begin to make their appearance on the infundibula in the form of minute pouches. The pulmonary arteries are derived from the sixth aortic arches. During the course of their development the lungs migrate in a caudal direction, so that by the time of birth the bifurcation of the trachea is opposite the fourth thoracic vertebra. As the lungs grow they project into that part of the celom which will ultimately form the pleural cavities, and the superficial layer of the mesoderm enveloping the lung rudiment expands on the growing lung and is converted into the pulmonary pleura.
External nose and the nasal cavity, which is divided by a septum into right and left nasal chambers.
External Nose (Nasus Externus; Outer Nose) is pyramidal in form, and its upper angle or root is connected directly with the forehead; its free angle is termed the apex. Its base is perforated by two elliptical orifices, the nares, separated from each other by an antero-posterior septum, the columna. The margins of the nares are provided with a number of stiff hairs, or vibrissæ, which arrest the passage of foreign substances carried with the current of air intended for respiration. The lateral surfaces of the nose form, by their union in the middle line, the dorsum nasi, the direction of which varies considerably in different individuals; the upper part of the dorsum is supported by the nasal bones, and is named the bridge. The lateral surface ends below in a rounded eminence, the ala nasi.
Structure.—The frame-work of the external nose is composed of bones and cartilages; it is covered by the integument, and lined by mucous membrane.
The bony frame-work occupies the upper part of the organ; it consists of the nasal bones, and the frontal processes of the maxillæ.
The cartilaginous frame-work (cartilagines nasi) consists of five large pieces, viz., the cartilage of the septum, the two lateral and the two greater alar cartilages, and several smaller pieces, the lesser alar cartilages. The various cartilages are connected to each other and to the bones by a tough fibrous membrane.
The cartilage of the septum (cartilago septi nasi) is somewhat quadrilateral in form, thicker at its margins than at its center, and completes the separation between the nasal cavities in front. Its anterior margin, thickest above, is connected with the nasal bones, and is continuous with the anterior margins of the lateral cartilages; below, it is connected to the medial crura of the greater alar cartilages by fibrous tissue. Its posterior margin is connected with the perpendicular plate of the ethmoid; its inferior margin with the vomer and the palatine processes of the maxillæ.
It may be prolonged backward (especially in children) as a narrow process, the sphenoidal process, for some distance between the vomer and perpendicular plate of the ethmoid. The septal cartilage does not reach as far as the lowest part of the nasal septum. This is formed by the medial crura of the greater alar cartilages and by the skin; it is freely movable, and hence is termed the septum mobile nasi.
The lateral cartilage (cartilago nasi lateralis; upper lateral cartilage) is situated below the inferior margin of the nasal bone, and is flattened, and triangular in shape. Its anterior margin is thicker than the posterior, and is continuous above with the cartilage of the septum, but separated from it below by a narrow fissure; its superior margin is attached to the nasal bone and the frontal process of the maxilla; its inferior margin is connected by fibrous tissue with the greater alar cartilage.
The greater alar cartilage (cartilago alaris major; lower lateral cartilage) is a thin, flexible plate, situated immediately below the preceding, and bent upon itself in such a manner as to form the medial and lateral walls of the naris of its own side. The portion which forms the medial wall (crus mediale) is loosely connected with the corresponding portion of the opposite cartilage, the two forming, together with the thickened integument and subjacent tissue, the septum mobile nasi. The part which forms the lateral wall (crus laterale) is curved to correspond with the ala of the nose; it is oval and flattened, narrow behind, where it is connected with the frontal process of the maxilla by a tough fibrous membrane, in which are found three or four small cartilaginous plates, the lesser alar cartilages (cartilagines alares minores; sesamoid cartilages). Above, it is connected by fibrous tissue to the lateral cartilage and front part of the cartilage of the septum; below, it falls short of the margin of the naris, the ala being completed by fatty and fibrous tissue covered by skin. In front, the greater alar cartilages are separated by a notch which corresponds with the apex of the nose.
Cartilages of the nose. Side view.
Cartilages of the nose, seen from below.
Bones and cartilages of septum of nose. Right side.
The muscles acting on the external nose have been described in the section on Myology.
The integument of the dorsum and sides of the nose is thin, and loosely connected with the subjacent parts; but over the tip and alæ it is thicker and more firmly adherent, and is furnished with a large number of sebaceous follicles, the orifices of which are usually very distinct.
The arteries of the external nose are the alar and septal branches of the external maxillary, which supply the alæ and septum; the dorsum and sides being supplied from the dorsal nasal branch of the ophthalmic and the infraorbital branch of the internal maxillary. The veins end in the anterior facial and ophthalmic veins.
The nerves for the muscles of the nose are derived from the facial, while the skin receives branches from the infratrochlear and nasociliary branches of the ophthalmic, and from the infraorbital of the maxillary.
the Nasal Cavity (Cavum Nasi; Nasal Fossa)—The
nasal chambers are situated one on either side of the median plane. They open
in front through the nares, and communicate behind through the choanæ
with the nasal part of the pharynx. The nares are somewhat pear-shaped
apertures, each measuring about
For the description of the bony boundaries of the nasal cavities, see pages 194 and 195.
Inside the aperture of the nostril is a slight dilatation, the vestibule, bounded laterally by the ala and lateral crus of the greater alar cartilage, and medially by the medial crus of the same cartilage. It is lined by skin containing hairs and sebaceous glands, and extends as a small recess toward the apex of the nose. Each nasal cavity, above and behind the vestibule, is divided into two parts: an olfactory region, consisting of the superior nasal concha and the opposed part of the septum, and a respiratory region, which comprises the rest of the cavity.
Lateral wall of nasal cavity.
Lateral Wall—On the lateral wall are the superior, middle, and inferior nasal conchæ, and below and lateral to each concha is the corresponding nasal passage or meatus. Above the superior concha is a narrow recess, the sphenoethmoidal recess, into which the sphenoidal sinus opens. The superior meatus is a short oblique passage extending about half-way along the upper border of the middle concha; the posterior ethmoidal cells open into the front part of this meatus. The middle meatus is below and lateral to the middle concha, and is continued anteriorly into a shallow depression, situated above the vestibule and named the atrium of the middle meatus. On raising or removing the middle concha the lateral wall of this meatus is fully displayed. On it is a rounded elevation, the bulla ethmoidalis, and below and in front of this is a curved cleft, the hiatus semilunaris.
The bulla ethmoidalis is caused by the bulging of the middle ethmoidal cells which open on or immediately above it, and the size of the bulla varies with that of its contained cells.
Lateral wall of nasal cavity; the three nasal conchæ have been removed.
The hiatus semilunaris is bounded inferiorly by the sharp concave margin of the uncinate process of the ethmoid bone, and leads into a curved channel, the infundibulum, bounded above by the bulla ethmoidalis and below by the lateral surface of the uncinate process of the ethmoid. The anterior ethmoidal cells open into the front part of the infundibulum, and this in slightly over 50 per cent. of subjects is directly continuous with the frontonasal duct or passage leading from the frontal air sinus; but when the anterior end of the uncinate process fuses with the front part of the bulla, this continuity is interrupted and the frontonasal duct then opens directly into the anterior end of the middle meatus.
Below the bulla ethmoidalis, and partly hidden by the inferior end of the uncinate process, is the ostium maxillare, or opening from the maxillary sinus; in a frontal section this opening is seen to be placed near the roof of the sinus. An accessory opening from the sinus is frequently present below the posterior end of the middle nasal concha. The inferior meatus is below and lateral to the inferior nasal concha; the nasolacrimal duct opens into this meatus under cover of the anterior part of the inferior concha.
Medial Wall or septum is frequently more or less deflected from the median plane, thus lessening the size of one nasal cavity and increasing that of the other; ridges or spurs of bone growing into one or other cavity from the septum are also sometimes present. Immediately over the incisive canal at the lower edge of the cartilage of the septum a depression, the nasopalatine recess, is seen. In the septum close to this recess a minute orifice may be discerned; it leads backward into a blind pouch, the rudimentary vomeronasal organ of Jacobson, which is supported by a strip of cartilage, the vomeronasal cartilage. This organ is well-developed in many of the lower animals, where it apparently plays a part in the sense of smell, since it is supplied by twigs of the olfactory nerve and lined by epithelium similar to that in the olfactory region of the nose.
The roof of the nasal cavity is narrow from side to side, except at its posterior part, and may be divided, from behind forward, into sphenoidal, ethmoidal, and frontonasal parts, after the bones which form it.
The floor is concave from side to side and almost horizontal antero-posteriorly; its anterior three-fourths are formed by the palatine process of the maxilla, its posterior fourth by the horizontal process of the palatine bone. In its anteromedial part, directly over the incisive foramen, a small depression, the nasopalatine recess, is sometimes seen; it points downward and forward and occupies the position of a canal which connected the nasal with the buccal cavity in early fetal life.
The Mucous Membrane (membrana mucosa nasi).—The nasal mucous membrane lines the nasal cavities, and is intimately adherent to the periosteum or perichondrium. It is continuous with the skin through the nares, and with the mucous membrane of the nasal part of the pharynx through the choanæ. From the nasal cavity its continuity with the conjunctiva may be traced, through the nasolacrimal and lacrimal ducts; and with the frontal, ethmoidal, sphenoidal, and maxillary sinuses, through the several openings in the meatuses. The mucous membrane is thickest, and most vascular, over the nasal conchæ. It is also thick over the septum; but it is very thin in the meatuses on the floor of the nasal cavities, and in the various sinuses.
Owing to the thickness of the greater part of this membrane, the nasal cavities are much narrower, and the middle and inferior nasal conchæ appear larger and more prominent than in the skeleton; also the various apertures communicating with the meatuses are considerably narrowed.
Structure of the Mucous Membrane. The epithelium covering the mucous membrane differs in its character according to the functions of the part of the nose in which it is found. In the respiratory region it is columnar and ciliated. Interspersed among the columnar cells are goblet or mucin cells, while between their bases are found smaller pyramidal cells. Beneath the epithelium and its basement membrane is a fibrous layer infiltrated with lymph corpuscles, so as to form in many parts a diffuse adenoid tissue, and under this a nearly continuous layer of small and larger glands, some mucous and some serous, the ducts of which open upon the surface. In the olfactory region the mucous membrane is yellowish in color and the epithelial cells are columnar and non-ciliated; they are of two kinds, supporting cells and olfactory cells. The supporting cells contain oval nuclei, which are situated in the deeper parts of the cells and constitute the zone of oval nuclei; the superficial part of each cell is columnar, and contains granules of yellow pigment, while its deep part is prolonged as a delicate process which ramifies and communicates with similar processes from neighboring cells, so as to form a net-work in the mucous membrane. Lying between the deep processes of the supporting cells are a number of bipolar nerve cells, the olfactory cells, each consisting of a small amount of granular protoplasm with a large spherical nucleus, and possessing two processes—a superficial one which runs between the columnar epithelial cells, and projects on the surface of the mucous membrane as a fine, hair-like process, the olfactory hair; the other or deep process runs inward, is frequently beaded, and is continued as the axon of an olfactory nerve fiber. Beneath the epithelium, and extending through the thickness of the mucous membrane, is a layer of tubular, often branched, glands, the glands of Bowman, identical in structure with serous glands. The epithelial cells of the nose, fauces and respiratory passages play an important role in the maintenance of an equable temperature, by the moisture with which they keep the surface always slightly lubricated.
Vessels and Nerves.—The arteries of the nasal cavities are the anterior and posterior ethmoidal branches of the ophthalmic, which supply the ethmoidal cells, frontal sinuses, and roof of the nose; the sphenopalatine branch of the $$$ which supplies the mucous membrane covering the conchæ, the meatuses and septum, the septal branch of the superior labial of the external maxillary; the infraorbital and alveolar branches of the internal maxillary, which supply the lining membrane of the maxillary sinus; and the pharyngeal branch of the same artery, distributed to the sphenoidal sinus. The ramifications of these vessels form a close plexiform net-work, beneath and in the substance of the mucous membrane.
The veins form a close cavernous plexus beneath the mucous membrane. This plexus is especially well-marked over the lower part of the septum and over the middle and inferior conchæ. Some of the veins open into the sphenopalatine vein; others join the anterior facial vein; some accompany the ethmoidal arteries, and end in the ophthalmic veins; and, lastly, a few communicate with the veins on the orbital surface of the frontal lobe of the brain, through the foramina in the cribriform plate of the ethmoid bone; when the foramen cecum is patent it transmits a vein to the superior sagittal sinus.
The lymphatics have already been described.
The nerves of ordinary sensation are: the nasociliary branch of the ophthalmic, filaments from the anterior alveolar branch of the maxillary, the nerve of the pterygoid canal, the nasopalatine, the anterior palatine, and nasal branches of the sphenopalatine ganglion.
The nasociliary branch of the ophthalmic distributes filaments to the forepart of the septum and lateral wall of the nasal cavity. Filaments from the anterior alveolar nerve supply the inferior meatus and inferior concha. The nerve of the pterygoid canal supplies the upper and back part of the septum, and superior concha; and the upper nasal branches from the sphenopalatine ganglion have a similar distribution. The nasopalatine nerve supplies the middle of the septum. The anterior palatine nerve supplies the lower nasal branches to the middle and inferior conchæ.
The olfactory, the special nerve of the sense of smell, is distributed to the olfactory region. Its fibers arise from the bipolar olfactory cells and are destitute of medullary sheaths. They unite in fasciculi which form a plexus beneath the mucous membrane and then ascend in grooves or canals in the ethmoid bone; they pass into the skull through the foramina in the cribriform plate of the ethmoid and enter the under surface of the olfactory bulb, in which they ramify and form synapses with the dendrites of the mitral cells.
Nerves of septum of nose. Right side
The Accessory Sinuses of the Nose (Sinus Paranasales)
The accessory sinuses or air cells of the nose are the frontal, ethmoidal, sphenoidal, and maxillary; they vary in size and form in different individuals, and are lined by ciliated mucous membrane directly continuous with that of the nasal cavities.
The Frontal Sinuses (sinus frontales),
situated behind the superciliary arches, are rarely symmetrical, and the septum
between them frequently deviates to one or other side of the middle line. Their
average measurements are as follows: height,
Coronal section of nasal cavities.
The Ethmoidal Air Cells (cellulæ ethmoidales) consist of numerous thin-walled cavities situated in the ethmoidal labyrinth and completed by the frontal, maxilla, lacrimal, sphenoidal, and palatine. They lie between the upper parts of the nasal cavities and the orbits, and are separated from these cavities by thin bony laminæ. On either side they are arranged in three groups, anterior, middle, and posterior. The anterior and middle groups open into the middle meatus of the nose, the former by way of the infundibulum, the latter on or above the bulla ethmoidalis. The posterior cells open into the superior meatus under cover of the superior nasal concha; sometimes one or more opens into the sphenoidal sinus. The ethmoidal cells begin to develop during fetal life.
The Sphenoidal Sinuses (sinus sphenoidales)
contained within the body of the sphenoid vary in size and shape; owing to the
lateral displacement of the intervening septum they are rarely symmetrical. The
following are their average measurements: vertical height,
Specimen from a child eight days old. By sagittal sections removing the lateral portion of frontal bone, lamina papyracea of ethmoid, and lateral portion of maxilla—the sinus maxillaris, cellulæ ethmoidales, anterior and posterior, infundibulum ethmoidale, and the primitive sinus frontalis are brought into view.
Specimen from a child one year, four months, and seven days old. Lateral view of frontal, ethmoidal, and maxillary sinus areas.
The Maxillary Sinus (sinus maxillaris; antrum of
Highmore), the largest of the accessory sinuses of the nose, is a pyramidal
cavity in the body of the maxilla. Its base is formed by the lateral wall of
the nasal cavity, and its apex extends into the zygomatic process. Its roof or
orbital wall is frequently ridged by the infra-orbital canal, while its floor
is formed by the alveolar process and is usually 1/2 to
Specimen from a child eight years, eight months, and one day old. Lateral view of frontal, ethmoidal and maxillary sinus areas, the lateral portion of each having been removed by sagittal cuts. Note that the sinus frontalis developed directly from the infundibulum ethmoidale.
Note also the incomplete septa in the sinus maxillaris.
The accessory sinuses or air cells of the nose are the frontal, ethmoidal, sphenoidal, and maxillary; they vary in size and form in different individuals, and are lined by ciliated mucous membrane directly continuous with that of the nasal cavities.
The Frontal Sinuses (sinus frontales),
situated behind the superciliary arches, are rarely symmetrical, and the septum
between them frequently deviates to one or other side of the middle line. Their
average measurements are as follows: height,
Coronal section of nasal cavities.
The Ethmoidal Air Cells (cellulæ ethmoidales) consist of numerous thin-walled cavities situated in the ethmoidal labyrinth and completed by the frontal, maxilla, lacrimal, sphenoidal, and palatine. They lie between the upper parts of the nasal cavities and the orbits, and are separated from these cavities by thin bony laminæ. On either side they are arranged in three groups, anterior, middle, and posterior. The anterior and middle groups open into the middle meatus of the nose, the former by way of the infundibulum, the latter on or above the bulla ethmoidalis. The posterior cells open into the superior meatus under cover of the superior nasal concha; sometimes one or more opens into the sphenoidal sinus. The ethmoidal cells begin to develop during fetal life.
The Sphenoidal Sinuses (sinus sphenoidales)
contained within the body of the sphenoid vary in size and shape; owing to the
lateral displacement of the intervening septum they are rarely symmetrical. The
following are their average measurements: vertical height,
Specimen from a child eight days old. By sagittal sections removing the lateral portion of frontal bone, lamina papyracea of ethmoid, and lateral portion of maxilla—the sinus maxillaris, cellulæ ethmoidales, anterior and posterior, infundibulum ethmoidale, and the primitive sinus frontalis are brought into view.
Specimen from a child one year, four months, and seven days old. Lateral view of frontal, ethmoidal, and maxillary sinus areas.
The Maxillary Sinus (sinus maxillaris; antrum of
Highmore), the largest of the accessory sinuses of the nose, is a pyramidal
cavity in the body of the maxilla. Its base is formed by the lateral wall of
the nasal cavity, and its apex extends into the zygomatic process. Its roof or
orbital wall is frequently ridged by the infra-orbital canal, while its floor
is formed by the alveolar process and is usually 1/2 to
Specimen from a child eight years, eight months, and one day old. Lateral view of frontal, ethmoidal and maxillary sinus areas, the lateral portion of each having been removed by sagittal cuts. Note that the sinus frontalis developed directly from the infundibulum ethmoidale.
1, Mandible. 2, Upper edge of the orbit. 3, Frontal sinus. 4, Maxillary sinus. 5, Dens of axis.
1, Superior orbital fissure. 2, Greater wing of sphenoid bone . 3, Lesser wing of sphenoid. 4, Frontal sinus. 5, Petrous bone.
1, Hard palate. 2, Maxillary sinus. 3, Orbit. 4, Frontal sinus. 5, Sphenoidal sinuses. 6, Pituitary fossa. 7, Posterior clinoid process. 8, Spinous process (Atlas). 9, Spinous process (Axis).
Sinus CT scan - Image 17
Sagittal reconstruction. 1, Nasal bone. 2, Frontal sinus. 3, Ethmoid sinuses. 4, Sphenoid sinus. 5, Inferior turbinate. 6, Hard palate.
Sinus CT scan - Image 19
Sagittal reconstruction. 1, Frontal sinus. 2, Ethmoid sinuses. 3, Sphenoid sinus. 4, clivus. 5, middle turbinate. 6, Inferior turbinate. 7, Hard palate.
Sinus CT scan - Image 9
Coronal reconstruction. 1, Orbital cavity. 2, Ethmoid sinuses. 3, Middle turbinate. 4, Inferior turbinate. 5, Right maxillary sinus. 6, Zygomatic arch. 7, Mandible.
Sinus CT scan - Image 12
Coronal reconstruction. 1, Frontal sinus. 2, Frontal bone. 3, Globe. 4, Maxillary sinus. 5, Nasal septum. 6, Inferior turbinate.
Sinus CT scan - Image 2
Axial multidetector CT image. 1, Globe. 2, Nasal septum. 3, Ethmoid sinuses. 4, Sphenoid sinus. 5, Pituitary gland. 6, dorsum sellae.
Sinus CT scan - Image 3
Axial multidetector CT image. 1, Globe. 2, Nasal septum. 3, Ethmoid sinuses. 4, Sphenoid sinus. 5, Clivus.
Sinus CT scan - Image 6
Axial multidetector CT image. 1, Maxillary sinus. 2, pterygoid process. 3, Rhinopharynx. 4, Mandible. 5, Atlas: anterior arch. 6, Odontoid process (dens) of the axis.
1, Mandible. 2, Upper edge of the orbit. 3, Frontal sinus. 4, Maxillary sinus. 5, Dens of axis.
1, Superior orbital fissure. 2, Greater wing of sphenoid bone . 3, Lesser wing of sphenoid. 4, Frontal sinus. 5, Petrous bone.
1, Hard palate. 2, Maxillary sinus. 3, Orbit. 4, Frontal sinus. 5, Sphenoidal sinuses. 6, Pituitary fossa. 7, Posterior clinoid process. 8, Spinous process (Atlas). 9, Spinous process (Axis).
Sinus CT scan - Image 17
Sagittal reconstruction. 1, Nasal bone. 2, Frontal sinus. 3, Ethmoid sinuses. 4, Sphenoid sinus. 5, Inferior turbinate. 6, Hard palate.
Sinus CT scan - Image 19
Sagittal reconstruction. 1, Frontal sinus. 2, Ethmoid sinuses. 3, Sphenoid sinus. 4, clivus. 5, middle turbinate. 6, Inferior turbinate. 7, Hard palate.
Sinus CT scan - Image 9
Coronal reconstruction. 1, Orbital cavity. 2, Ethmoid sinuses. 3, Middle turbinate. 4, Inferior turbinate. 5, Right maxillary sinus. 6, Zygomatic arch. 7, Mandible.
Sinus CT scan - Image 12
Coronal reconstruction. 1, Frontal sinus. 2, Frontal bone. 3, Globe. 4, Maxillary sinus. 5, Nasal septum. 6, Inferior turbinate.
Sinus CT scan - Image 2
Axial multidetector CT image. 1, Globe. 2, Nasal septum. 3, Ethmoid sinuses. 4, Sphenoid sinus. 5, Pituitary gland. 6, dorsum sellae.
Sinus CT scan - Image 3
Axial multidetector CT image. 1, Globe. 2, Nasal septum. 3, Ethmoid sinuses. 4, Sphenoid sinus. 5, Clivus.
Sinus CT scan - Image 6
Axial multidetector CT image. 1, Maxillary sinus. 2, pterygoid process. 3, Rhinopharynx. 4, Mandible. 5, Atlas: anterior arch. 6, Odontoid process (dens) of the axis.
The Digestive Apparatus (Apparatus Digestorius; Organs Of Digestion)
The apparatus for the digestion of the food consists of the digestive tube and of certain accessory organs.
The Digestive
Tube (alimentary canal) is a musculomembranous tube, about
The accessory organs are the teeth, for purposes of mastication; the three pairs of salivary glands—the parotid, submandibular, and sublingual—the secretion from which mixes with the food in the mouth and converts it into a bolus and acts chemically on one of its constituents; the liver and pancreas, two large glands in the abdomen, the secretions of which, in addition to that of numerous minute glands in the walls of the alimentary canal, assist in the process of digestion.
The Development of the Digestive Tube.—The primitive digestive tube consists of two parts, viz.: (1) the fore-gut, within the cephalic flexure, and dorsal to the heart; and (2) the hind-gut, within the caudal flexure. Between these is the wide opening of the yolk-sac, which is gradually narrowed and reduced to a small foramen leading into the vitelline duct. At first the fore-gut and hind-gut end blindly. The anterior end of the fore-gut is separated from the stomodeum by the buccopharyngeal membrane the hind-gut ends in the cloaca, which is closed by the cloacal membrane.
The Mouth.—The mouth is developed partly from the stomodeum, and partly from the floor of the anterior portion of the fore-gut. By the growth of the head end of the embryo, and the formation of the cephalic flexure, the pericardial area and the buccopharyngeal membrane come to lie on the ventral surface of the embryo. With the further expansion of the brain, and the forward bulging of the pericardium, the buccopharyngeal membrane is depressed between these two prominences. This depression constitutes the stomodeum. It is lined by ectoderm, and is separated from the anterior end of the fore-gut by the buccopharyngeal membrane. This membrane is devoid of mesoderm, being formed by the apposition of the stomodeal ectoderm with the fore-gut entoderm; at the end of the third week it disappears, and thus a communication is established between the mouth and the future pharynx. No trace of the membrane is found in the adult; and the communication just mentioned must not be confused with the permanent isthmus faucium. The lips, teeth, and gums are formed from the walls of the stomodeum, but the tongue is developed in the floor of the pharynx.
The visceral arches extend in a ventral direction between the stomodeum and the pericardium; and with the completion of the mandibular arch and the formation of the maxillary processes, the mouth assumes the appearance of a pentagonal orifice. The orifice is bounded in front by the fronto-nasal process, behind by the mandibular arch, and laterally by the maxillary processes. With the inward growth and fusion of the palatine processes, the stomodeum is divided into an upper nasal, and a lower buccal part. Along the free margins of the processes bounding the mouth cavity a shallow groove appears; this is termed the primary labial groove, and from the bottom of it a downgrowth of ectoderm takes place into the underlying mesoderm. The central cells of the ectodermal downgrowth degenerate and a secondary labial groove is formed; by the deepening of this, the lips and cheeks are separated from the alveolar processes of the maxillæ and mandible.
The Salivary Glands.—The salivary glands arise as buds from the epithelial lining of the mouth; the parotid appears during the fourth week in the angle between the maxillary process and the mandibular arch; the submandibular appears in the sixth week, and the sublingual during the ninth week in the hollow between the tongue and the mandibular arch.
The Tongue is developed in the floor of the pharynx, and consists of an anterior or buccal and a posterior or pharyngeal part which are separated in the adult by the V-shaped sulcus terminalis. During the third week there appears, immediately behind the ventral ends of the two halves of the mandibular arch, a rounded swelling named the tuberculum impar, which was described by His as undergoing enlargement to form the buccal part of the tongue. More recent researches, however, show that this part of the tongue is mainly, if not entirely, developed from a pair of lateral swellings which rise from the inner surface of the mandibular arch and meet in the middle line. The tuberculum impar is said to form the central part of the tongue immediately in front of the foramen cecum, but Hammar insists that it is purely a transitory structure and forms no part of the adult tongue. From the ventral ends of the fourth arch there arises a second and larger elevation, in the center of which is a median groove or furrow. This elevation was named by His the furcula, and is at first separated from the tuberculum impar by a depression, but later by a ridge, the copula, formed by the forward growth and fusion of the ventral ends of the second and third arches. The posterior or pharyngeal part of the tongue is developed from the copula, which extends forward in the form of a V, so as to embrace between its two limbs the buccal part of the tongue. At the apex of the V a pit-like invagination occurs, to form the thyroid gland, and this depression is represented in the adult by the foramen cecum of the tongue. In the adult the union of the anterior and posterior parts of the tongue is marked by the V-shaped sulcus terminalis, the apex of which is at the foramen cecum, while the two limbs run lateralward and forward, parallel to, but a little behind, the vallate papillæ.
The Palatine Tonsils are developed from the dorsal angles of the second branchial pouches. The entoderm which lines these pouches grows in the form of a number of solid buds into the surrounding mesoderm. These buds become hollowed out by the degeneration and casting off of their central cells, and by this means the tonsillar crypts are formed. Lymphoid cells accumulate around the crypts, and become grouped to form the lymphoid follicles; the latter, however, are not well-defined until after birth.
The Further Development of the Digestive Tube.—The upper part of the fore-gut becomes dilated to form the pharynx, in relation to which the branchial arches are developed (see page 65); the succeeding part remains tubular, and with the descent of the stomach is elongated to form the esophagus. About the fourth week a fusiform dilatation, the future stomach, makes its appearance, and beyond this the gut opens freely into the yolk-sac. The opening is at first wide, but is gradually narrowed into a tubular stalk, the yolk-stalk or vitelline duct. Between the stomach and the mouth of the yolk-sac the liver diverticulum appears. From the stomach to the rectum the alimentary canal is attached to the notochord by a band of mesoderm, from which the common mesentery of the gut is subsequently developed. The stomach has an additional attachment, viz., to the ventral abdominal wall as far as the umbilicus by the septum transversum. The cephalic portion of the septum takes part in the formation of the diaphragm, while the caudal portion into which the liver grows forms the ventral mesogastrium. The stomach undergoes a further dilatation, and its two curvatures can be recognized, the greater directed toward the vertebral column and the lesser toward the anterior wall of the abdomen, while its two surfaces look to the right and left respectively. Behind the stomach the gut undergoes great elongation, and forms a V-shaped loop which projects downward and forward; from the bend or angle of the loop the vitelline duct passes to the umbilicus. For a time a considerable part of the loop extends beyond the abdominal cavity into the umbilical cord, but by the end of the third month it is withdrawn within the cavity. With the lengthening of the tube, the mesoderm, which attaches it to the future vertebral column and carries the bloodvessels for the supply of the gut, is thinned and drawn out to form the posterior common mesentery. The portion of this mesentery attached to the greater curvature of the stomach is named the dorsal mesogastrium, and the part which suspends the colon is termed the mesocolon. About the sixth week a diverticulum of the gut appears just behind the opening of the vitelline duct, and indicates the future cecum and vermiform process. The part of the loop on the distal side of the cecal diverticulum increases in diameter and forms the future ascending and transverse portions of the large intestine. Until the fifth month the cecal diverticulum has a uniform caliber, but from this time onward its distal part remains rudimentary and forms the vermiform process, while its proximal part expands to form the cecum. Changes also take place in the shape and position of the stomach. Its dorsal part or greater curvature, to which the dorsal mesogastrium is attached, grows much more rapidly than its ventral part or lesser curvature to which the ventral mesogastrium is fixed. Further, the greater curvature is carried downward and to the left, so that the right surface of the stomach is now directed backward and the left surface forward, a change in position which explains why the left vagus nerve is found on the front, and the right vagus on the back of the stomach. The dorsal mesogastrium being attached to the greater curvature must necessarily follow its movements, and hence it becomes greatly elongated and drawn lateralward and ventralward from the vertebral column, and, as in the case of the stomach, the right surfaces of both the dorsal and ventral mesogastria are now directed backward, and the left forward. In this way a pouch, the bursa omentalis, is formed behind the stomach, and this increases in size as the digestive tube undergoes further development; the entrance to the pouch constitutes the future foramen epiploicum or foramen of Winslow. The duodenum is developed from that part of the tube which immediately succeeds the stomach; it undergoes little elongation, being more or less fixed in position by the liver and pancreas, which arise as diverticula from it. The duodenum is at first suspended by a mesentery, and projects forward in the form of a loop. The loop and its mesentery are subsequently displaced by the transverse colon, so that the right surface of the duodenal mesentery is directed backward, and, adhering to the parietal peritoneum, is lost. The remainder of the digestive tube becomes greatly elongated, and as a consequence the tube is coiled on itself, and this elongation demands a corresponding increase in the width of the intestinal attachment of the mesentery, which becomes folded.
At this stage the small and large intestines are attached to the vertebral column by a common mesentery, the coils of the small intestine falling to the right of the middle line, while the large intestine lies on the left side.
The gut is now rotated upon itself, so that the large intestine is carried over in front of the small intestine, and the cecum is placed immediately below the liver; about the sixth month the cecum descends into the right iliac fossa, and the large intestine forms an arch consisting of the ascending, transverse, and descending portions of the colon—the transverse portion crossing in front of the duodenum and lying just below the greater curvature of the stomach; within this arch the coils of the small intestine are disposed. Sometimes the downward progress of the cecum is arrested, so that in the adult it may be found lying immediately below the liver instead of in the right iliac region.
Further changes take place in the bursa omentalis and in the common mesentery, and give rise to the peritoneal relations seen in the adult. The bursa omentalis, which at first reaches only as far as the greater curvature of the stomach, grows downward to form the greater omentum, and this downward extension lies in front of the transverse colon and the coils of the small intestine. Above, before the pleuro-peritoneal opening is closed, the bursa omentalis sends up a diverticulum on either side of the esophagus; the left diverticulum soon disappears, but the right is constricted off and persists in most adults as a small sac lying within the thorax on the right side of the lower end of the esophagus. The anterior layer of the transverse mesocolon is at first distinct from the posterior layer of the greater omentum, but ultimately the two blend, and hence the greater omentum appears as if attached to the transverse colon. The mesenteries of the ascending and descending parts of the colon disappear in the majority of cases, while that of the small intestine assumes the oblique attachment characteristic of its adult condition.
The lesser omentum is formed, as indicated above, by a thinning of the mesoderm or ventral mesogastrium, which attaches the stomach and duodenum to the anterior abdominal wall. By the subsequent growth of the liver this leaf of mesoderm is divided into two parts, viz., the lesser omentum between the stomach and liver, and the falciform and coronary ligaments between the liver and the abdominal wall and diaphragm.
The Rectum and Anal Canal.—The hind-gut is at first prolonged backward into the body-stalk as the tube of the allantois; but, with the growth and flexure of the tail-end of the embryo, the body-stalk, with its contained allantoic tube, is carried forward to the ventral aspect of the body, and consequently a bend is formed at the junction of the hind-gut and allantois. This bend becomes dilated into a pouch, which constitutes the entodermal cloaca; into its dorsal part the hind-gut opens, and from its ventral part the allantois passes forward. At a later stage the Wolffian and Müllerian ducts open into its ventral portion. The cloaca is, for a time, shut off from the anterior by a membrane, the cloacal membrane, formed by the apposition of the ectoderm and entoderm, and reaching, at first, as far forward as the future umbilicus. Behind the umbilicus, however, the mesoderm subsequently extends to form the lower part of the abdominal wall and symphysis pubis. By the growth of the surrounding tissues the cloacal membrane comes to lie at the bottom of a depression, which is lined by ectoderm and named the ectodermal cloaca.
The entodermal cloaca is divided into a dorsal and a ventral part by means of a partition, the urorectal septum, which grows downward from the ridge separating the allantoic from the cloacal opening of the intestine and ultimately fuses with the cloacal membrane and divides it into an anal and a urogenital part. The dorsal part of the cloaca forms the rectum, and the anterior part of the urogenital sinus and bladder. For a time a communication named the cloacal duct exists between the two parts of the cloaca below the urorectal septum; this duct occasionally persists as a passage between the rectum and urethra. The anal canal is formed by an invagination of the ectoderm behind the urorectal septum. This invagination is termed the proctodeum, and it meets with the entoderm of the hind-gut and forms with it the anal membrane. By the absorption of this membrane the anal canal becomes continuous with the rectum. A small part of the hind-gut projects backward beyond the anal membrane; it is named the post-anal gut, and usually becomes obliterated and disappears.
Note.Sometimes this condition persists throughout life, and it is then found that the duodenum does not cross from the right to the left side of the vertebral column, but lies entirely on the right side of the median plane, where it is continued into the jejunum; the arteries to the small intestine (aa. intestinales) also arise from the right instead of the left side of the superior mesenteric artery.
The Mouth (Cavum Oris; Oral Or Buccal Cavity)
The cavity of the mouth is placed at the commencement of the digestive tube it is a nearly oval-shaped cavity which consists of two parts: an outer, smaller portion, the vestibule, and an inner, larger part, the mouth cavity proper.
The Vestibule (vestibulum oris) is a slit-like space, bounded externally by the lips and cheeks; internally by the gums and teeth. It communicates with the surface of the body by the rima or orifice of the mouth. Above and below, it is limited by the reflection of the mucous membrane from the lips and cheeks to the gum covering the upper and lower alveolar arch respectively. It receives the secretion from the parotid salivary glands, and communicates, when the jaws are closed, with the mouth cavity proper by an aperture on either side behind the wisdom teeth, and by narrow clefts between opposing teeth.
The Mouth Cavity Proper (cavum oris proprium) is bounded laterally and in front by the alveolar arches with their contained teeth; behind, it communicates with the pharynx by a constricted aperture termed the isthmus faucium. It is roofed in by the hard and soft palates, while the greater part of the floor is formed by the tongue, the remainder by the reflection of the mucous membrane from the sides and under surface of the tongue to the gum lining the inner aspect of the mandible. It receives the secretion from the submandibular and sublingual salivary glands.
Structure.—The mucous membrane lining the mouth is continuous with the integument at the free margin of the lips, and with the mucous lining of the pharynx behind; it is of a rosepink tinge during life, and very thick where it overlies the hard parts bounding the cavity. It is covered by stratified squamous epithelium.
The Lips (labia oris), the two fleshy folds which surround the rima or orifice of the mouth, are formed externally of integument and internally of mucous membrane, between which are found the Orbicularis oris muscle, the labial vessels, some nerves, areolar tissue, and fat, and numerous small labial glands. The inner surface of each lip is connected in the middle line to the corresponding gum by a fold of mucous membrane, the frenulum—the upper being the larger.
The Labial Glands (glandulœ labiales) are situated between the mucous membrane and the Orbicularis oris, around the orifice of the mouth. They are circular in form, and about the size of small peas; their ducts open by minute orifices upon the mucous membrane. In structure they resemble the salivary glands.
The Cheeks (buccæ) form the sides of the face, and are continuous in front with the lips. They are composed externally of integument; internally of mucous membrane; and between the two of a muscular stratum, besides a large quantity of fat, areolar tissue, vessels, nerves, and buccal glands.
Structure.—The mucous membrane lining the cheek is reflected above and below upon the gums, and is continuous behind with the lining membrane of the soft palate. Opposite the second molar tooth of the maxilla is a papilla, on the summit of which is the aperture of the parotid duct. The principal muscle of the cheek is the Buccinator; but other muscles enter into its formation, viz., the Zygomaticus, Risorius, and Platysma.
The buccal glands are placed between the mucous membrane and Buccinator muscle: they are similar in structure to the labial glands, but smaller. About five, of a larger size than the rest, are placed between the Masseter and Buccinator muscles around the distal extremity of the parotid duct; their ducts open in the mouth opposite the last molar tooth. They are called molar glands.
The Gums (gingivœ) are composed of dense fibrous tissue, closely connected to the periosteum of the alveolar processes, and surrounding the necks of the teeth. They are covered by smooth and vascular mucous membrane, which is remarkable for its limited sensibility. Around the necks of the teeth this membrane presents numerous fine papillæ, and is reflected into the alveoli, where it is continuous with the periosteal membrane lining these cavities.
The Palate (palatum) forms the roof of the mouth; it consists of two portions, the hard palate in front, the soft palate behind.
The Hard Palate (palatum durum) is bounded in front and at the sides by the alveolar arches and gums; behind, it is continuous with the soft palate. It is covered by a dense structure, formed by the periosteum and mucous membrane of the mouth, which are intimately adherent. Along the middle line is a linear raphæ, which ends anteriorly in a small papilla corresponding with the incisive canal. On either side and in front of the raphé the mucous membrane is thick, pale in color, and corrugated; behind, it is thin, smooth, and of a deeper color; it is covered with stratified squamous epithelium, and furnished with numerous palatal glands, which lie between the mucous membrane and the surface of the bone.
The Soft Palate (palatum molle) is a movable fold, suspended from the posterior border of the hard palate, and forming an incomplete septum between the mouth and pharynx. It consists of a fold of mucous membrane enclosing muscular fibers, an aponeurosis, vessels, nerves, adenoid tissue, and mucous glands. When occupying its usual position, i. e., relaxed and pendent, its anterior surface is concave, continuous with the roof of the mouth, and marked by a median raphé. Its posterior surface is convex, and continuous with the mucous membrane covering the floor of the nasal cavities. Its upper border is attached to the posterior margin of the hard palate, and its sides are blended with the pharynx. Its lower border is free. Its lower portion, which hangs like a curtain between the mouth and pharynx is termed the palatine velum.
Hanging from the middle of its lower border is a small, conical, pendulous process, the palatine uvula; and arching lateralward and downward from the base of the uvula on either side are two curved folds of mucous membrane, containing muscular fibers, called the arches or pillars of the fauces.
The Teeth (dentes) —Man is provided with two sets of teeth, which make their appearance at different periods of life. Those of the first set appear in childhood, and are called the deciduous or milk teeth. Those of the second set, which also appear at an early period, may continue until old age, and are named permanent.
The deciduous teeth are twenty in number: four incisors, two canines, and four molars, in each jaw.
The permanent teeth are thirty-two in number: four incisors, two canines, four premolars, and six molars, in each jaw.
The dental formulæ may be represented as follows:
Deciduous Teeth. Upper jaw Lower jaw
mol. 2 2
can. 1 1
in. 2 2
in. 2 2
can. 1 1
mol. 2 2
Total 20
Permanent Teeth. Upper jaw Lower jaw
mol. 3 3
pr.mol. 2 2
can. 1 1
in. 2 2
in. 2 2
can. 1 1
pr.mol. 2 2
mol. 3 3
Total 32
General Characteristics.—Each tooth consists of three portions: the crown, projecting above the gum; the root, imbedded in the alveolus; and the neck, the constricted portion between the crown and root.
The roots of the teeth are firmly implanted in depressions within the alveoli; these depressions are lined with periosteum which invests the tooth as far as the neck. At the margins of the alveoli, the periosteum is continuous with the fibrous structure of the gums.
In consequence of the curve of the dental arch, terms such as anterior and posterior, as applied to the teeth, are misleading and confusing. Special terms are therefore used to indicate the different surfaces of a tooth: the surface directed toward the lips or cheek is known as the labial or buccal surface; that directed toward the tongue is described as the lingual surface; those surfaces which touch neighboring teeth are termed surfaces of contact. In the case of the incisor and canine teeth the surfaces of contact are medial and lateral; in the premolar and molar teeth they are anterior and posterior.
The superior dental arch is larger than the inferior, so that in the normal condition the teeth in the maxillæ slightly overlap those of the mandible both in front and at the sides. Since the upper central incisors are wider than the lower, the other teeth in the upper arch are thrown somewhat distally, and the two sets do not quite correspond to each other when the mouth is closed: thus the upper canine tooth rests partly on the lower canine and partly on the first premolar, and the cusps of the upper molar teeth lie behind the corresponding cusps of the lower molar teeth. The two series, however, end at nearly the same point behind; this is mainly because the molars in the upper arch are the smaller.
The Permanent Teeth (dentes permanentes) —The Incisors (dentes incisivi; incisive or cutting teeth) are so named from their presenting a sharp cutting edge, adapted for biting the food. They are eight in number, and form the four front teeth in each dental arch.
The crown is directed vertically, and is chisel-shaped, being bevelled at the expense of its lingual surface, so as to present a sharp horizontal cutting edge, which, before being subjected to attrition, presents three small prominent points separated by two slight notches. It is convex, smooth, and highly polished on its labial surface; concave on its lingual surface, where, in the teeth of the upper arch, it is frequently marked by an inverted V-shaped eminence, situated near the gum. This is known as the basal ridge or cingulum. The neck is constricted. The root is long, single, conical, transversely flattened, thicker in front than behind, and slightly grooved on either side in the longitudinal direction.
The upper incisors are larger and stronger than the lower, and are directed obliquely downward and forward. The central ones are larger than the lateral, and their roots are more rounded.
The lower incisors are smaller than the upper: the central ones are smaller than the lateral, and are the smallest of all the incisors. They are placed vertically and are somewhat bevelled in front, where they have been worn down by contact with the overlapping edge of the upper teeth. The cingulum is absent.
The Canine Teeth (dentes canini) are four in number, two in the upper, and two in the lower arch, one being placed laterally to each lateral incisor. They are larger and stronger than the incisors, and their roots sink deeply into the bones, and cause well-marked prominences upon the surface.
The crown is large and conical, very convex on its labial surface, a little hollowed and uneven on its lingual surface, and tapering to a blunted point or cusp, which projects beyond the level of the other teeth. The root is single, but longer and thicker than that of the incisors, conical in form, compressed laterally, and marked by a slight groove on each side.
The upper canine teeth (popularly called eye teeth) are larger and longer than the lower, and usually present a distinct basal ridge.
The lower canine teeth (popularly called stomach teeth) are placed nearer the middle line than the upper, so that their summits correspond to the intervals between the upper canines and the lateral incisors.
The Premolars or Bicuspid teeth (dentes præmolares) are eight in number, four in each arch. They are situated lateral to and behind the canine teeth, and are smaller and shorter than they.
The crown is compressed antero-posteriorly, and surmounted by two pyramidal eminences or cusps, a labial and a lingual, separated by a groove; hence their name bicuspid. Of the two cusps the labial is the larger and more prominent. The neck is oval. The root is generally single, compressed, and presents in front and behind a deep groove, which indicates a tendency in the root to become double. The apex is generally bifid.
The upper premolars are larger, and present a greater tendency to the division of their roots than the lower; this is especially the case in the first upper premolar.
The Molar Teeth (dentes molares) are the largest of the permanent set, and their broad crowns are adapted for grinding and pounding the food. They are twelve in number; six in each arch, three being placed posterior to each of the second premolars.
The crown of each is nearly cubical in form, convex on its buccal and lingual surfaces, flattened on its surfaces of contact; it is surmounted by four or five tubercles, or cusps, separated from each other by a crucial depression; hence the molars are sometimes termed multicuspids. The neck is distinct, large, and rounded.
The Deciduous Teeth (dentes decidui; temporary or milk teeth) —The deciduous are smaller than, but, generally speaking, resemble in form, the teeth which bear the same names in the permanent set. The hinder of the two molars is the largest of all the deciduous teeth, and is succeeded by the second premolar. The first upper molar has only three cusps—two labial, one lingual; the second upper molar has four cusps. The first lower molar has four cusps; the second lower molar has five. The roots of the deciduous molars are smaller and more divergent than those of the permanent molars, but in other respects bear a strong resemblance to them.
Structure of the Teeth.—On making a vertical section of a tooth, a cavity will be found in the interior of the crown and the center of each root; it opens by a minute orifice at the extremity of the latter. This is called the pulp cavity, and contains the dental pulp, a loose connective tissue richly supplied with vessels and nerves, which enter the cavity through the small aperture at the point of each root. Some of the cells of the pulp are arranged as a layer on the wall of the pulp cavity; they are named the odontoblasts of Waldeyer, and during the development of the tooth, are columnar in shape, but later on, after the dentin is fully formed, they become flattened and resemble osteoblasts. Each has two fine processes, the outer one passing into a dental canaliculus, the inner being continuous with the processes of the connective-tissue cells of the pulp matrix.
The solid portion of the tooth consists of (1) the ivory or dentin, which forms the bulk of the tooth; (2) the enamel, which covers the exposed part of the crown; and (3) a thin layer of bone, the cement or crusta petrosa, which is disposed on the surface of the root.
The dentin (substantia eburnea; ivory) forms the principal mass of a tooth. It is a modification of osseous tissue, from which it differs, however, in structure. On microscopic examination it is seen to consist of a number of minute wavy and branching tubes, the dental canaliculi, imbedded in a dense homogeneous substance, the matrix.
The dental canaliculi (dentinal tubules) are placed parallel with one another, and open at their inner ends into the pulp cavity. In their course to the periphery they present two or three curves, and are twisted on themselves in a spiral direction. These canaliculi vary in direction: thus in a tooth of the mandible they are vertical in the upper portion of the crown, becoming oblique and then horizontal in the neck and upper part of the root, while toward the lower part of the root they are inclined downward. In their course they divide and subdivide dichotomously, and, especially in the root, give off minute branches, which join together in loops in the matrix, or end blindly. Near the periphery of the dentin, the finer ramifications of the canaliculi terminate imperceptibly by free ends. The dental canaliculi have definite walls, consisting of an elastic homogeneous membrane, the dentinal sheath of Neumann, which resists the action of acids; they contain slender cylindrical prolongations of the odontoblasts, first described by Tomes, and named Tomes’ fibers or dentinal fibers.
The matrix (intertubular dentin) is translucent, and contains the chief part of the earthy matter of the dentin. In it are a number of fine fibrils, which are continuous with the fibrils of the dental pulp. After the earthy matter has been removed by steeping a tooth in weak acid, the animal basis remaining may be torn into laminæ which run parallel with the pulp cavity, across the direction of the tubes. A section of dry dentin often displays a series of somewhat parallel lines—the incremental lines of Salter. These lines are composed of imperfectly calcified dentin arranged in layers. In consequence of the imperfection in the calcifying process, little irregular cavities are left, termed interglobular spaces. Normally a series of these spaces is found toward the outer surface of the dentin, where they form a layer which is sometimes known as the granular layer. They have received their name from the fact that they are surrounded by minute nodules or globules of dentin. Other curved lines may be seen parallel to the surface. These are the lines of Schreger, and are due to the optical effect of simultaneous curvature of the dentinal fibers.
Chemical Composition.—According to Berzelius and von Bibra, dentin consists of 28 parts of animal and 72 parts of earthy matter. The animal matter is converted by boiling into gelatin. The earthy matter consists of phosphate of lime, carbonate of lime, a trace of fluoride of calcium, phosphate of magnesium, and other salts.
Prepared by
A.V. MIZ