Introduction to Human Anatomy.

 

Initial stages of human embryogenesis.

 

Study about germ layers

Contents

The contents of human anatomy, its place among biological sciences and importance for medicine. Anatomic sciences and adjacent disciplines. Methodology of morphological sciences. Descriptive, functional, causal and systemic, structural principle of study of a body structure. Methods of anatomic researches. The anatomic nomenclature. Initial stages of human embryogenesis. Study about germ layers

THE TERM human anatomy comprises a consideration of the various structures which make up the human organism. In a restricted sense it deals merely with the parts which form the fully developed individual and which can be rendered evident to the naked eye by various methods of dissection. Regarded from such a standpoint it may be studied by two methods: (1) the various structures may be separately considered—systematic anatomy; or (2) the organs and tissues may be studied in relation to one another—topographical or regional anatomy.   1  It is, however, of much advantage to add to the facts ascertained by naked-eye dissection those obtained by the use of the microscope. This introduces two fields of investigation, viz., the study of the minute structure of the various component parts of the body—histology—and the study of the human organism in its immature condition, i. e., the various stages of its intrauterine development from the fertilized ovum up to the period when it assumes an independent existence—embryology. Owing to the difficulty of obtaining material illustrating all the stages of this early development, gaps must be filled up by observations on the development of lower forms—comparative embryology, or by a consideration of adult forms in the line of human ancestry—comparative anatomy. The direct application of the facts of human anatomy to the various pathological conditions which may occur constitutes the subject of applied anatomy. Finally, the appreciation of structures on or immediately underlying the surface of the body is frequently made the subject of special study—surface anatomy.   

SYSTEMATIC ANATOMY.—The various systems of which the human body is composed are grouped under the following headings:

Osteology—the bony system or skeleton. Syndesmology—the articulations or joints. Myology—the muscles. With the description of the muscles it is convenient to include that of the fasciæ which are so intimately connected with them. Angiology—the vascular system, comprising the heart, bloodvessels, lymphatic vessels, and lymph glands. Neurology—the nervous system. The organs of sense may be included in this system. Splanchnology—the visceral system. Topographically the viscera form two groups, viz., the thoracic viscera and the abdomino-pelvic viscera. The heart, a thoracic viscus, is best considered with the vascular system. The rest of the viscera may be grouped according to their functions: (a) the respiratory apparatus; (b) the digestive apparatus; and (c) the urogenital apparatus. Strictly speaking, the third subgroup should include only such components of the urogenital apparatus as are included within the abdomino-pelvic cavity, but it is convenient to study under this heading certain parts which lie in relation to the surface of the body, e. g., the testes and the external organs of generation.

For descriptive purposes the body is supposed to be in the erect posture, with the arms hanging by the sides and the palms of the hands directed forward. The median plane is a vertical antero-posterior plane, passing through the center of the trunk. This plane will pass approximately through the sagittal suture of the skull, and hence any plane parallel to it is termed a sagittal plane. A vertical plane at right angles to the median plane passes, roughly speaking, through the central part of the coronal suture or through a line parallel to it; such a plane is known as a frontal plane or sometimes as a coronal plane. A plane at right angles to both the median and frontal planes is termed a transverse plane.   

The terms anterior or ventral, and posterior or dorsal, are employed to indicate the relation of parts to the front or back of the body or limbs, and the terms superior or cephalic, and inferior or caudal, to indicate the relative levels of different structures; structures nearer to or farther from the median plane are referred to as medial or lateral respectively.   

The terms superficial and deep are strictly confined to descriptions of the relative depth from the surface of the various structures; external and internal are reserved almost entirely for describing the walls of cavities or of hollow viscera. In the case of the limbs the words proximal and distal refer to the relative distance from the attached end of the limb. Anatomy is an unusual subject because the material we use is human. This gives, at one and the same time, a fascination and a repugnance, simply because the material is human.

“The study of anatomy by dissection requires in its practitioners the effective suspension or suppression of many normal physical and emotional responses to the wilful mutilation of the body of another human being” – Richardson.

In other words, in normal society, outside the medical school we would probably be locked up for dissection, and its not very nice anyway, is it? The name given to the ability to suppress physical and emotional responses is 'clinical detachment'. Clinical detachment is the way in which we deal, as anatomists, with the repugnant, the distasteful, and what, if we did it to a living human being, would be criminal. It is acquired slowly, bit by bit, and to different extents. William Harvey, discoverer of circulation of the blood, dissected both his father and his sister. Few of us would wish to be so clinically detached.

If we did it to a living human being is the key phrase. The cadaver is not a living human being but neither is it a pound of offal.. Perhaps we should examine our attitude to our own, and other peoples' bodies.

Man has always been fascinated by the interior of his body. The first written documents to survive are clay tablets from around 4000 BC in Nineveh. The cuneiform script impressed upon these tablets can be translated, and tells us many things. Some tablets are inventories for warehouses, some are the equivalent of laundry lists, and some tell us about the insides of men and animals opened in a form of fortune telling - trying to predict the future.

The next landmark was anatomical detail set down by Galen in the second century AD. This was meagre, distorted and bore little relationship to the dissected body.

In the Renaissance a change of attitude occurred: in Italy this took the form of patronage and the setting up of schools of anatomy, notably at Padua, and the work of the first two great anatomists, Leonardo da Vinci and Versalius. Da Vinci's work was hidden until the late eighteenth century but Versalius De Humani Corpus Fabrica, published in 1543 was the first anatomy textbook as we know it, drawn from life (or death), accurate and painstaking.

England, as usual in things European, lagged behind, but Scotland granted royal patronage to the Edinburgh College of Surgeons and Barbers in 1506. England followed suit in 1540. (Surgeons thus have a long connection with barbers: this is because medical men denied them professional status, and leads to the inverted snobbery of the consultant surgeon whose title is still MR . The low status of the surgeon, which dated from the Council of Tours edict in 1163 whereby the church abhorred the spilling of blood. Ecclesiastics who were also medics were thus discouraged from surgery, although they continued to practice medicine, and subcontracted surgical procedures to others, often barbers, who performed blood letting, tooth drawing and later midwifery.)

It is at this point that things get complicated and that Anatomy starts to get a bad name. Part of the patronage given by James IV of Scotland was the bodies of certain executed criminals for dissection. In England Henry VIII granted the annual right to the bodies of four hanged felons. Charles II later increased this to six . Now bodies had to come from somewhere, but the conjoining of anatomy and hanging offences was very bad news, and the basis of an association which lasted until the first Anatomy act in 1832. Dissection was now a recognised punishment, a fate worse than death to be added to hanging for the worst offenders.

The dissections performed on hanged felons were public: indeed part of the punishment was the delivery from hangman to surgeons at the gallows following public execution, and later public exhibition of the open body itself. The punishment replaced the earlier hanging drawing and quartering, in which the four quarters were exhibited on spikes in various parts of the city, and differed only in that it was performed by medical men, and, incidentally that anatomical knowledge was obtained. This state of affairs was accepted by surgeons because it was, oddly, good for their image to achieve royal patronage and to be linked with the law. In France, incidentally surgeons acquired respectability by the back door. In 1687 surgeons performed a successful operation for anal fistula on Louis XIV. It was successful, probably because they practised for a year on lesser mortals with the same complaint. In 1752 an act was passed allowing dissection of all murderers as an alternative to hanging in chains. This was a grisly fate, the tarred body being suspended in a cage until it fell to pieces. The object of this and dissection was to deny a grave. After the act the number of available bodies increased, and the act itself was pro anatomy in that the execution had to follow smartly upon conviction, and the body conveyed immediately to the surgeons. Dissection was described as 'a further terror and peculiar Mark of Infamy' and 'in no case whatsoever shall the body of any murderer be suffered to be buried'. The rescue, or attempted rescue of the corpse was punishable by transportation for seven years.

The act benefited anatomists immediately. In 1775 the royal college of surgeons acquired eight bodies at once before rigor mortis had set in: one was 'put in an attitude and allowed to stiffen' by William Hunter, Professor of Anatomy, flayed and a mould prepared. A cast from this is still on view at the Royal Society of Arts in London.

Hunter was a key figure in Anatomy. He ran his own private anatomy school in Great Windmill St in London where he thought in the 'Parisian manner', each student having access to an individual corpse. He also set up a museum of human and comparative anatomy. The Company of Surgeons was 'intellectually stagnant' at this time, had no hall and was more interested as a City livery company in giving public dinners than offering public dissection. Despite this, in the period between 1701-1744, 24 lecturers in anatomy are known to have been active in London alone. The private schools had no legal status and no legal source of material. The question was, where did Hunter, his brother and the other anatomists setting up private schools get their cadavers - certainly not from official sources. The suspicion, probably justified, was that people were being paid to obtain corpses. The corpse was now a commodity: it had cash value and could be bought and sold. Harvey's solution of keeping it in the family did not become popular: most anatomists bought from the gallows or the grave.

Agents representing surgeons would bargain with condemned prisoners not under sentence of dissection (remember this only happened for murder: hanging was in vogue for stealing a sheep or even a loaf) : occasionally prisoners struck a bargain to pay expenses, to provide for a family or to buy the customary decent apparel for the hanging. Supply was unreliable, however: riots at public hangings became common, partly because of the paltry nature of hanging events, partly from superstition. The body was often reclaimed by relatives and the unpopular anatomists stoned, defeated and out of pocket. Competition was often so fierce that a rival anatomy school carried off the body. Dissection was unpopular and other medical uses were to be found for a recently hung body - the cure of scofula, goitre, wens, ulcers, bleeding tumours, cancers and withered limbs for example. To prevent riots and disorder the Sheriff of London took all bodies of hanged men, except those sentenced to dissection, into his own custody and handed them to the relatives for burial.

However in 1826 592 bodies were dissected by students at London anatomy schools. Most of these must have come from grave robbers. The earliest grave robbers seem to have been the surgeons themselves. In 1721 a clause was inserted into apprentices indentures issued by the Edinburgh college of surgeons forbidding trainee surgeons from becoming involved in exhumation. Later, students accompanied professional body snatchers as observers. In Scotland it was possible to pay fees in corpses rather than in cash. By the 1780s the work was left to the professionals -Ressurectionists or Sack' em up men. A professional gang of 15 body snatchers was rounded up in Lambeth in 1795. They worked, winter only, serving 'eight surgeons of repute' from 30 burial grounds. Corpses cost two guineas and a crown - £2.35 and children six shillings for the first foot and nine pence for each extra inch. By 1820 the cost was up to 20 guineas for an unremarkable corpse for dissection. Freaks cost a lot more. O'Brien, the Irish giant, well over seven feet tall, who died in 1783 was bought by John Hunter for £500, despite his wish to be buried at sea to avoid such a fate. He now stands in the entrance of the Royal College of Surgeons in London.

Oddly body snatching was not an offence. The body was not regarded as property, and, once dead, could not be owned or stolen. Occasionally a body snatcher would be whipped, on unclear legal grounds. Only if property - such as a shroud was removed was the robber a thief.

The grave robbers job was easier if the graves of the poor were robbed. Pit burials, or mass graves were common, and often a large square pit up to 20 feet deep would be excavated, filled with coffins gradually over a period of weeks then closed. Stealing bodies from such graves cannot have been difficult. The wealthy, of course could buy a metal coffin (1781), Bribgeman's patent cast iron coffin (1818) or use a mortsafe - a kind of cage of iron bars surrounding a tomb. They could also, and did, employ guards, even armed guards to ensure their eternal rest. The poor, acting in concert to reduce the cost often had a parish mortsafe or 'jankers' where bodies were kept until too high for the anatomist to use.

The demise of the body snatcher is perhaps one of the first cases of consumerism. Since the law was unable or unwilling to help, because of the lack of a clear offence, it was left to the public to intervene. Thus in 1828 two medical students caught attempting to snatch a body were committed to gaol at their own request as they were threatened by a large crowd. The following afternoon a crowd of several hundreds 'assembled round the gaol , provided with axes'. In Yarmouth, Hereford, Greenwich and Lambeth (we are now in the age of steam, and rapid reliable transport, at least by sea) similar scenes ensued. A full scale riot broke out in an Aberdeen anatomy school in 1832 when a dog unearthed human remains. The School was looted and burned. The crowd, estimated at 20,000 denied access to the fire engine.

By the time the Aberdeen Riots took place at least 16 citizens of Edinburgh had been murdered in order to stock the anatomy school. Burke and Hare gained a poor living in Edinburgh mending shoes. When a lodger at Mrs Hare's lodging house died the pair sold the body to Dr Knox's anatomy school for £7.50. Another lodger fell ill, and was befuddled with whisky , smothered and sold for £10. Fifteen more followed.

The riots, the murders and public opinion meant that something had to be done and the outcome was the 1832 Anatomy Act which was a key issue in the election of 1832. A key figure behind this was Jeremy Bentham, founder of University College London. His idea was essentially that anyone applying to a hospital for treatment was in effect giving permission for the use of their body, in the event of a poor result, being available for dissection, followed by Christian burial. Although forgoing a Christian burial Bentham was publicly dissected at University College in 1828. There is a sub text to this. Anyone applying to a hospital for treatment meant, in effect the poor who could not afford to pay a doctor. Hospital also meant workhouse. After much argument with Peel, the Prime Minister and political manoeuvring designed so that the death rates in the workhouse should not be made public the bill became law. The situation was now this: the bodies of those maintained by the state (i.e. in Workhouses) if not claimed by relatives (for burial at their expense) became the property of the Anatomist. The fate of these bodies had become, and still is, anatomical examination - not dissection. Administration was by an Inspector of Anatomy, working for the Home Office. Unsurprisingly the residents of workhouses, unconsulted, were not happy with the act, but powerless to do much about it. Many evaded examination by signing a declaration that they did not wish to be dissected: the supply from workhouses was unexpectedly low: there were riots: there was scandal, maladministration and indecency and plain mistakes. Burial services and coffins were often rudimentary. Burial clubs became common - like a Christmas Club - pay so much a week for your funeral. Just before World War 1 ten percent of the income of women in Lambeth was set aside for 'Industrial insurance'. There is still a dread amongst the older generation of a 'pauper's funeral' The only change to the act, however, was in response to repeated failure of the anatomists to bury remains within the stipulated period: the period was extended in 1871.

We operated under the 1832 act until very recently. What has changed? Well, the workhouse has gone. From the Anatomists point of view this meant that the supply of material declined: there were shortages in the 1920s. The Inspector of Anatomy at the time suggested 'a modest fee of five shillings' to officials in mental homes - by then the main source of supply.

At this point something odd happened, perhaps allied to the rise of socialism and atheism. There was continued outcry against the bodies of the poor being used, and against token burial services in token coffins. But there was also a rise in donations. From almost zero before world war one, to 5% between the wars, then rising again after world war two to almost 100%. The cause of this is unknown: it parallels a rise in cremation rather than burial and perhaps tokens a change in our attitude to our bodies. Perhaps it parallels the demise of the paupers funeral and the idea that poverty and misfortune could qualify a person for dismemberment against their will. Who knows ? But all bodies dissected in Leeds are now donations.

So what does donation entail? Around 100 people a year from the area contact us wanting details of this philanthropic act. We ask only that a letter stating their wish is placed with their effects. At the time of death we are informed and, if the next of kin agree, the body (which is technically their property) is donated to us. If the donation is accepted by a Licensed Teacher ( reasons for refusal include post mortem examination, notifiable disease, gross over- or underweight and certain diseases which change the anatomy of the body). The deceased , having been certified as dead, is collected by an Undertaker and transferred to our mortuary. After a statutory period (there are constant stories in the papers of the certified dead waking in the mortuary) the deceased is given a coded label, undressed, shaved and embalmed with a mixture of alcohol, formaldehyde and phenol in water. Embalming fluid is introduced via an artery, usually the femoral artery in the leg. The process of embalming renders the cadaver sterile, discourages decomposition and prevents the spread of disease. The cadaver is then wrapped an placed in a refrigerator until used.

Certain provisions of the Anatomy Act are taken very seriously in this University. First we are obliged, after a statutory period, to bury or cremate all the remains of Mr X, unless he has given consent that certain portions are retained as museum specimens. We do not wish to confuse bits of Mr X with bits of Mr Y. At this point we should distinguish between the kinds of anatomical specimens you will see first of all the cadaver which students may dissect. Secondly the prosection, where the dissection has already been done for you. These are either wet specimens ie embalmed or plastinated -embedded in a plastic resin which leaves them flexible but dry to the touch. Thirdly the museum specimen or pot, which, as it name implies is sealed in a jar. Fourthly dried bones. Fifthly radiographs, CAT scans etc.

In order to keep all pieces of Mr X together the rule is that he stays on the same table until finished with. Parts will then be removed in labelled bags and placed in the mortuary. After a statutory period all remains will be collected together, placed in a coffin and buried or cremated according to the wishes of the deceased. Members of staff attend funerals as a mark of respect. We must also remember that Mr X was someone's husband, father, uncle, lover. and treat him accordingly.

A few rules of elementary hygiene are also necessary in anatomy classes. Wear a white coat, tie your hair back if it is long and wear plastic gloves if you wish. You will not catch anything from the corpse, but the embalming fluid irritates some people's skin and human fat smells. If you come to classes in street clothes you are guaranteed a seat on the bus home. Do not eat or drink in anatomy class. The other resource which we have not mentioned is you, the student. You are young, healthy and alive. Wherever anatomy can be demonstrated on the living we do so. You will therefore find yourselves called upon to act as models for your fellows for all the bits conveniently seen from the outside - surface anatomy. This means that you should be appropriately dressed for the relevant classes and be prepared to remove clothing as necessary. So we are back to Richardson's problem of suppression of physical and emotional responses. We try to help you with this by a first class which is really compare and contrast yourselves with cadavers: we hope that this will breed familiarity, and familiarity will in turn breed respect rather than contempt.

Methods of study. Dissection of a fixed cadaver is the most important tool of anatomists. The dissection may be done by you, the students (and you will have opportunities to practice this skill during the course) or by someone else on your behalf, to produce prosections which show particular regions or features. Prosections save you time, but I suspect that dissection leaves a longer lasting impression of structure.

Living anatomy is the observation of the living body at rest or in action. This has both drawbacks and plus points. Our own bodies (or those of colleagues) are always available to see and feel, and we are younger and more muscular than dissecting room specimens, who are a. dead from natural causes and hence b. usually old and c. embalmed. Some of your patients will be old, but few will be dead or embalmed. So the examination of a patient is an exercise in living anatomy. Living anatomy is sometimes called surface anatomy, because that is what we see - so the obvious drawback is that some parts cannot be seen or felt in the living.

But instruments do exist to allow us to extend the view from the outside on patients. These are usually called -scopes: endoscopes, proctoscopes, bronchoscopes etc. all allow further examination. Nowadays these are often fibre optic devices aided by computer visualisation, and can allow a good view of the gall bladder or the inside of the knee joint.

We can also add a range of indirect imaging techniques. The first of these was probably radiology, the directing of a beam of x-rays at a subject and the measurement of the intensity of what passes through, usually by means of darkening a photographic plate. Different tissues absorb radiation to different degrees, and the pattern of densities can record position shape and size of bones, fat, gas filled structures and so on. Interpretation is often a little difficult because structures at some distance from the source are magnified as the rays diverge and all structures are in focus, and so appear piled on top of each other in two dimensions. A plain radiograph can be enhanced by filling relevant bits of the patient with contrast medium, which is opaque to x-rays. This can be injected into a blood vessel or swallowed to outline parts of the gut.

Radio isotope imaging is a variant of this where the contrast medium is replaced by a radio labelled substance avidly taken up by the target tissue - for instance radio iodine can be used to target the thyroid gland. Tomography, is a newer technique in which source and photographic plate are moved in relation to the subject. Computer Assisted Tomography (CAT) is an even more sophisticated technique in which both x- ray source and detector (replacing film) are moved around the body, producing a data stream which is interpreted by a computer as a series of images equivalent to cross sections through the body at fixed intervals. The drawback is of course that X rays are now known to be harmful, inducing mutation and tissue damage.

Alternatives include: -ultrasound which reflects from boundary layers between tissues of different densities  -magnetic resonance imaging (MRI) produces images according the atomic structure of their major components, by subjecting them to a strong collapsing magnetic force. Again pictures equivalent to cross sections of the body are

The anatomic nomenclature. Anatomy is the study of the structure of the body. Derived from the Greek to cut up: the Latin 'to cut up' gives us dissect. Structure determines function and vice versa. Understanding the links between structure and function is intellectually more satisfying than learning lists, and makes long term retention easier. The abnormal patterns seen in disease are also related to anatomy: the transmission of stress from outstretched hand to trunk determines the location of skeletal fractures. The structure of the mouth determines the route of puss from a dental abscess. During your course we shall continually stress both the relationship between structure and function and the relationship between structure and disease. Under the general heading of anatomy are several subdivisions. Embryology examines development of adult structure from fertilised ovum. Cytology deals with the structure of individual cells. Histology deals with aggregations of cells, tissues, or aggregations of tissues, organs. Neuroanatomy deals with the elaborate connections of nerve cells. Gross anatomy deals with those structures that can be seen without a microscope. We must also not neglect comparative anatomy. Man is an animal and his structure is often more easily understood with reference to his relatives. For instance the skull contains air sinuses: two alternative theories suggest that these may a. reduce weight and b. act as resonators for the voice. Comparative anatomy tells us that other vertebrates have sinuses, even those which make no sounds. Birds such as geese, which make long migratory flights, have extensive sinuses, in the skull and elsewhere.

Vocabulary. Anatomy has a very specialised vocabulary, much of it inherited from Latin, Greek and Arabic, and used in a very precise way. Medical students usually double their vocabulary during training, and most of the new words will come in the next two years.

There is a standard list of terms, in Latin, which has the disadvantage that virtually no-one uses it. More often we use an anglicised version of these names. Our clinical colleagues either use alternative versions or outdated ones (depending on when they trained). And on top of this is the so-called eponymous nomenclature, calling things after their discoverer, or your boss or folk hero. This is frowned upon as it is unhelpful - Madonna's ligament or Minogue's disease doesn't tell us much about it.

Major parts of the body. Anatomical usage follows general for most of the main parts, head neck, trunk. The limbs are a little different. The Anatomist calls these the upper and lower limbs, and arm means between shoulder and elbow, and leg between knee and ankle. We subdivide the trunk into thorax, above the diaphragm and abdomen, below it.

The anatomical position. For descriptive purposes the body is always imagined to be in the anatomical position, standing erect, arms by sides, palms of hands facing forwards. In this position directions are given by superior, inferior, anterior, posterior. These are equivalent to the zoologists cephalad, caudad, ventral and dorsal. Thus the eyes are always superior to the mouth, even if the patient is lying down or standing on his head. These terms are not quite equivalent to above, below, in front of and behind. To a layman an acrobats feet are above her head when she is dangling from a trapeze: to an anatomist they are inferior.

Other dimensions are referred to the midline - median, medial or lateral, or to their closeness to the body surface, superficial or deep. In the limbs structures near the trunk are proximal, those further away are distal. We have a problem with the hands and feet: the palms of the hands resemble the soles of the feet and the thumb is equivalent to the great toe. But the palmar surface of the hand faces anteriorly and the back is dorsal. In the foot we defy logic and call the inferior surface plantar (equivalent to palmar) and the superior surface dorsal, even though it faces upwards. But we are still not out of the wood because the great toe is medial but the thumb is lateral. To get around this the term preaxial is often used to describe the thumb or great toe side. Postaxial is the little toe or little finger side. The axis referred to runs to the tip of the middle finger or the second toe. The other small problem, the penis, is described in it's erect position, so that its dorsal surface faces anteriorly and superiorly when detumescent.

We also need to define planes, mutually at right angles. The horizontal plane is clear enough: the other two are a little less so. The sagittal plane (L. sagitta, an arrow) probably refers to the sagittal suture which runs from anterior to posterior in the newborn skull, and has an arrowhead in the form of the frontal fontanelle. Coronal is also difficult since it means crown, and I always think of a crown as being horizontal. But this is an older usage, as in the crown of an arch or a tooth, or the road, meaning something more like a halo.

Once again these refer to the anatomical position.

Now that we can describe the body at rest we can also deal with movement.

abduction is movement of any part away from the midline in the coronal plain

adduction is return to the midline flexion is moving anything in the sagittal plane

extension is straightening it again.

lateral flexion is bending in the coronal plane

rotation occurs around a vertical axis, or the main axis of the limb. If we rotate the head to the right we end up facing right. For the limbs we still use the displacement of the anterior aspect i.e. lateral rotation moves the palm laterally. The shoulder is a good joint to illustrate movement because it is so free. The slide shows what we can do, and how we describe it.

Hand and foot again pose problems because of their distinctive orientation. The hand has a rather unusual movement whereby the thumb can be brought to lie medially: in fact this crosses the bones of the forearm. The anatomical position of the hand is called supine, the reverse prone, so this movement is pronation reverse supination.

Abduction and adduction of the digits are refereed to the axis of the hand or foot, which remember pass through the middle finger and the second toe. We also have a thumb problem. Finger nails are posterior, but that of the thumb lies at right angles to the others. The thumb normally lies with its palmar surface facing medially. Flexion and extension are thus in a coronal plane while abduction and adduction are sagittal. The thumb also has another important movement, opposition which brings its palmar surface in contact with the palmar surface of the fingers.

The feet also bring problems, so we talk of dorsiflexion and plantar flexion and, a unique foot movement inversion and eversion as the soles are made to point towards each other or away.

Variability in anatomy. One important fact which an anatomist must recognise is that no two of us, even identical twins are exactly alike. The structure of the body varies with age, race, sex, genetic, diversity, environmental history (especially during growth)

Age. Although this is a whole field in itself it is important to recognise the commonest changes due to age, since you will be looking mainly at aged cadavers and young, fit adults. Bear in mind that an 80 year old will differ in these respects: connective tissue - less elasticity - wrinkles cartilage - less elasticity - degenerative changes such as osteo-arthritis with associated changes. Costal cartilages often replaced by bone: bony spurs develop in unusual places. Bone - becomes brittle, reduced in size with less activity. Muscle - ditto, plus deposition of fat. Heart and blood vessels - arteries become tortuous, walls become furred up with atheroma. Left ventricle is enlarged as consequence of load. Veins often varicose. Nervous system - Often small strokes will cause paralysis and reduction in size of some muscles.

Race- This is a tricky one because of its emotive content, and because of the difficulty in defining race since the invention of the bicycle, steamship, jumbo jet etc. have done much to cause intermingling. Carefully noting the distinction between racism and Racialism we can say that there are obvious differences in skin and hair colour, hair type, eye colour, etc. and some subtle but small differences in anatomical measurements.

Sex - The two sexes obviously differ in their reproductive organs: they also differ in many other respects: although variability is quite large within a sex height, weight and muscle mass will differ significantly. Males also have narrower hips and broader shoulders. Females have more dermal fat, distributed differently. Facial and body hair also differs.

Genetic and other variation - congenital anomalies - There is quite a high level of genetic and environmental variation which leads to the presence of extra fingers, a single kidney, or an extra rib or so. This may be genetical or due to the exposure of the fetus to something unpleasant during pregnancy - x-rays, medicaments, viruses. Superimposed upon this is the variation due to habit - a regular swimmer will have a better developed upper body than his or her classmates: a smoker may have inferior lung capacity.