Lesson # 6

Brachial plexus, composition, topography, distribution of short branches.

Vascular-nervous fascicle of axilla

Long branches of brachial plexus, topography and distribution of branches on arm, forearm and hand

Lesson # 33

Theme 1. Brachial plexus, composition, topography, distribution of short branches.

Vascular-nervous fascicle of axilla

 

One of the most important characteristics of living substances is their capacity to respond to stimuli. Every living organism receives stimuli from its environment and responds to such stimuli by corresponding reactions which link the organism to the environment. Metabolic processes within the organism itself, in turn, create a number of stimuli to which the organism must also react In higher multicellular organisms the area receiving the stimulus and the reacting organ are connected by the nervous system.

Branching into all the organs and tissues, the nervous system binds and integrates all parts of the organism into a single, unified whole. Consequontly, the nervous system is “an indescribably complex and fine instru­ment, of relations involving the connection of numerous parts of the organism between one another and with the organism as a whole in a complex system with an infinite number of external influences” (I.P. Pavlov).

The activity of the nervous system is based on the reflex (I.M. Sechenov). “This means that a nervous receptor receives a signal from an agent of the external or internal world of the organism. This signal is transformed into a nerve process, in a phenomenon of nervous stimulation. The nerve impulse¹ passes along nerve fibres, as along wires, to the central nervous system and, from there, along established connections of other wires to the organ itself where it is transformed, in turn, into a specific process of the cells of this organ” (Pavlov).

The basic anatomical element of the nervous system is the nerve cell which, together with all the processes arising from it, is called the neuron. A long axial cylindrical process, called the axon or neurite, arises from the body of the cell in one direction. Short branched processes called dendrites lead in the other direction.

Nervous impulse inside the neuron flows from the dendrites to the cell body and from there to the axon; the axons convey the nervous impulse- away from the cell body. The conduct of the nerve impulse from one neuron l,o another is accomplished by means of specially built end apparatuses or synapses (Gk synaptein to join). Axosomatic connections of neurons in which the branches of one neuron approach the cell body of another neuron, can also be distinguished, as can axodendritic connections in which contact is accomplished by the dendrites of nerve cells. These latter are phylogenetically younger and are highly developed in the upper layers of the cortex, which are also phylogenetically more recent and functionally more sophisticated. These axodendritic connections play a role in the redistribution of nerve

impulses in the cortex and evidently represent the morphological basis of tem­porary connections in conditioned-reflex activity. Axosomatic connections prevail in the spinal cord and subcortical formations.

The intermittent flow of nerve conduction throughout the body allows for a great variety of connections. Thus, the nervous system is composed of a complex of neurons which come into contact with one another but never grow together^[1]. Consequently, the nervous impulse that arises in one part of the body is conveyed along the processes of nerve cells from one neuron to a second, from there to a third, and so on. A clear example of the connection established between organs through the neurons is the reflex arc which forms the basis of the reflex, the simplest and at the same time most fundamental reaction of the nervous system.

The simple reflex arc (Fig. 88) consists of at least two neurons, one of which connects with a sensory surface (the skin, for instance) and the other, which, with its axon, ends in a muscle (or a gland). When the sensory surfaco is stimulated, the nervous impulse passes centripetally along the neuron connected to it to the reflex centre where the synapse of both neurons is

ocated. Here the nervous impulse is transferred to the other neuron and directed centrilugally to the muscle or gland. As a result the muscle contracts or the secretion of the gland changes. Quite often a third internuncial neuron, which serves as a transmitting station from the sensory route to the motor route, is included in the simple reflex arc. Besides the simple (three-member) reflex arc there are complex multineuronal reflex arcs passing through different levels of the brain, including the cerebral cortex. In man and other higher animals neurons also form temporary reflex connections of the highest order on the basis of simple and complex reflexes. These temporary reflex con­nections are known as conditioned reflexes (Pavlov).

Thus, the elements of the nervous system may be classified as one of three kinds according to function.

1.  Receptors transform the energy of the external stimulus into a nerve process; the receptors are connected with afferent (centripetal or receptor) neurons, which transmit the triggered excitation (nerve impulse) toward the centre; the analysis begins from this phenomenon (Pavlov).

2.  Conductors are internuncial or connecting neurons which accomplish the contact, i.e. the transfer of the nerve impulse from the centripetal to the centrifugal neuron and the transformation of the impulse received by the centre into an external reaction. This synthesis “evidently represents the phenomenon of the nerve connector” (Pavlov). This is why Pavlov calls this neuron the connector.

3.  Efferent (centrifugal) neurons implement response reactions (motor or secretory) by conducting the nervous impulse from the centre to the effector (the producer of the effect or the action) at the periphery, i.e. to the working organ (muscle, gland). This is why this neuron is also called the effector neuron. The receptors are stimulated by three sensory surfaces, or receptor fields, of the organism: (1) the external skin surface of the body (exteroceptive field) through the sense organs which are genetically related to the skin and receive stimuli from the environment; (2) the internal surfaces of the body (interoceptive field) stimulated mostly by chemical substances entering the internal cavities; and (3) the thickness of the walls of the body itself (pro­prioceptive fields) where the bones, muscles, and other organs are laid out and produce stimuli received by special receptors. The receptors from such fields are connected with afferent neurons which reach the centre and transfer there to various efferent conductors by a very complicated system of conduc­tors. These efferent conductors produce various effects in conjunction with the working organs. Besides the reflex arc, a reflex circle has been found recently which participates as a basic component of nervous system activity.

Modern cybernetics has established the common feedback principle of connections in the control and coordination of processes in both modern automatons and living organisms. From this viewpoint a feedback connection can be distinguished in the nervous system between the working organ and the nerve centres. This phenomenon [called feedback afferentation (Anokhin) involves the transmission of impulses about the activity of the organ at any given moment from the working organ to the central nervous system. When the centres of the nervous system send efferent impulses to the executive organ, certain actions (movement, secretion) are triggered in this organ. These actions, in turn, stimulate nervous (sensory) impulses which return along afferent routes to the spinal cord and brain signalling that a certain action has just been performed by the working organ. Thus, the essence of feedback afferentation, is, figuratively speaking, a report to the centre that its command has been fulfilled by the periphery. When the hand reaches for an object, for example, the eyes constantly measure the distance between the hand and the object and dispatch the information as afferent signals to the brain. A contact is made in the brain with efferent neurons which convey motor impulses to the muscles of the hand reaching for the object. At the same time the muscles act upon the receptors within them to transmit con­tinuous sensitive signals to the brain and thus report on the position of the hand at every moment. This two-way signalization along the reflex circuits continues until the distance between the hand and the object is reduced to zero, i.e. until the hand grasps the object. The action of the working organ is thus constantly self-controlled by the mechanism of feedback afferentation, which functions as a closed circuit in the following succession: from the centre (the instrument setting the programme of action) to the effector (motor) to the tool (working organ) to the receptor (receiver) and back to the centre.

Such a closed circuit of reflexes in the central nervous system guarantees all the complex correction of the processes taking place in the organism no matter what changes may occur in the internal and external environment. Without the feedback mechanism living organisms would fail to adapt reasonably to the environment. Thus, in addition to the disconnected reflex arc which forms the basis of the nervous system, there are the closed reflex circuits that facilitate feedback afferentation of the working organ with the centres of the nervous system and that explain the reflex coordination of all its activity.

The unified human nervous system is conditionally divided into two parts corresponding to the two principal parts of the organism—vegetative and animal: (1) the vegetative nervous system innervates the internal organs, the endocrine system, and the smooth muscles of the skin, heart, and vessels, i.e. the organs of vegetative life which create the internal media of the organ­ism; (2) the animal nervous system controls the striated musculature of the skeleton and certain internal organs (tongue, larynx, pharynx) and primarily innervates the organs of animal life. The animal nervous system is also inaptly called the somatic system, meaning soma, i.e. the body itself.¹ I''or the most part it controls the functions connecting the organism with the environment, provides the sensitivity of the organism (through the sense organs), and the movements of the muscles of the skeleton. The limitations of such a provisional classification are obvious since the vegetative nervous system is related to the innervation of all the organs, including the s oxnatic organs, participating in their nutrition (trophies) and determining the tonus of the skeletal muscles.

Pavlov as well as K.M. Bykov and his students (V.N. Chernigovsky and others) demonstrated that the activity of all the internal organs and vessels depends on the cerebral cortex.

The vegetative part of the nervous system is, in turn, divided into the sympathetic and parasympathetic systems. The former system innervates the entire body while the parasympathetic system innervates only certain parts of it (see p. 171).

In addition to this structural classification the nervous system can be classified topographically into central and peripheral systems. The central nervous system consists of the spinal cord and brain made up of grey and white matter; the peripheral system includes all other components, i.e. the nerve roots, ganglia, plexuses, nerves, and peripheral nerve endings. The grey matter of the spinal cord and the brain is an accumulation of nerve cells together with the nearest branches and their processes called nerve centres. The nerve centre is “an accumulation and cohesion of nerve cells” (Pavlov). The white matter consists of nerve fibres (processes of nerve cells, axons) covered by a myelin sheath (which explains the white colour) linking the different centres together, i.e. the conducting pathways. Both the central and peripheral parts of the nervous system contain elements of its animal and vegetative components, thus uniting the nervous system as a whole. Its most highly developed section, which controls all the processes in the body, both animal and vegetative, is the cortex of the brain.

The nerve trunks are divided according to the place where they branch off from the central nervous system: the spinal nerves (nn. spinales) branch off from the spinal cord while the cranial nerves (nn. craniales) arise from the brain.

The discussed patterns of phylogenesis determine the embryogenesis of the human nervous system. The nervous system originates from the outer germinal layer of the embryo, or the ectoderm (see Vol.I, Introduction). The ectoderm forms a longitudinal thickening called the medullary or neural plate (Fig. 90) which is bounded on the sides by the remaining part of the ectoderm, the skin or horny layer. The medullary (neural) plate soon trans­forms into a medullary (neural) groove whose margins (medullary or neural folds) are gradually raised, approach each other, and fuse so converting the groove into a tube (neural tube). After fusion of the margins the neural tube separates completely from the skin ectoderm and the mesoderm grows be­tween them. The neural tube is the rudiment of the central part of the nervous system. The posterior, more or less uniform, end of the tube forms the rudi­ment of the spinal cord, while the expanded anterior end is separated by constrictions into three primary brain vesicles from which develops the brain in all its complexity.

At first the neural plate consists only of a single layer of epithelial cells. During its closure to form the neural tube the number of cells in the wall of the tube increases as a result of which three layers are formed: an inner layer (facing the cavity of the tube) from which the epithelial lining of the cerebral cavities is derived (the ependyma of the central canal of the spinal cord and the ventricles of the brain); a middle layer which gives rise to the grey matter of the brain (the nerve cells, neuroblasts); and, finally, an outer layer almost devoid of cell nuclei which develops into the white matter (processes of the nerve cells, neurites, or axons). Bundles of the neuroblast axons spread

either in the thickness of the neural tube to form the white matter or leave it to pass into the mesoderm and then become joined with the young muscle cells (myoblasts). In this manner the motor nerves arise.

The sensory nerves arise from the rudiments of the spinal ganglia already noticeable on the margins of the neural groove where it is continuous with the horny layer. When the groove has been converted into the neural tube the rudiments are displaced to the midline of its dorsal surface. The cells of these rudiments then move ventrally and are again arranged on the sides of the neural tube to form the neural crests. Both crests are shaped like a string of beads according to the segments of the dorsal surface of the embryo as a result of which a series of spinal ganglia (ganglia spinalia s. interverte- bralia) form on each side. In the cephalic part of the neural tube they reach only to the level of the posterior brain vesicle where they form the rudiments of the ganglia of the sensory cranial nerves. Neuroblasts develop in the gan­glionic rudiments in the form of bipolar nerve cells one of whose processes pierces the neural tube while the other passes to. the periphery and becomes the sensory nerve. Owing to fusion of both processes for some distance from their origin, the bipolar cells are converted to false unipolar cells possessing a single process which separates to form the letter “T”; these cells are char­acteristic of the intervertebral ganglia of the adult. The central processes of the cells penetrate the spinal cord and form the posterior roots of the spinal nerves, while the peripheral processes grow ventrally and compose (together with the efferent fibres which had left the spinal cord and formed the anterior root) a mixed spinal nerve. The neural crests also give rise to the rudiments of the vegetative system (this is discussed in detail on

 

 

The spinal nerves (nn. spinales) are located in regular order (neuro- meres) corresponding to the myotomes (myomeres) of the trunk and alternate with the segments of the spine; every nerve is attended by a corresponding area of skin (dermatome).

Man has 31 pairs of spinal nerves: 8 pairs of cervical, 12 pairs of thor­acic, 5 pairs of lumbar, 5 pairs of sacral and 1 pair of coccygeal nerves (see Fig. 91). Every spinal nerve branches off from the spinal cord in two roots: the dorsal or posterior (sensory) root, and the ventral or anterior (motor) root. Both roots are joined in one trunk, or funiculus which passes from the spine through an intervertebral orifice. Near and somewhat externally of the place where the roots join, the posterior root forms the ganglion spinale or ganglion intervertehrale in which the anterior motor root does not participate. Since both roots are joined the spinal nerves are mixed nerves; they contain sensory (afferent) fibres from the cells of the spinal ganglia, motor (efferent) fibres from the cells of the anterior horn, and also vegetative fibres from the cells of the lateral horns emerging from the spinal cord as part of the anterior root.

In the opinion of certain authors vegetative fibres are also contained in the posterior root. The vegetative fibres which pass through the roots into the animal nerves, ensure such processes in the soma as trophies, vasculo- motor reactions, etc.

In Gyclostomatae (lampreys) both roots continue into separate nerves, motor and sensory. In the further progress of evolution the nerves converge and merge so that the separate passage is preserved only for the roots, while the nerves become mixed.

On emerging from the intervertebral orifice every cerebrospinal nerve divides, according to two parts of the myotome (dorsal and ventral), into two branches:

(1)   the posterior, dorsal branch (ramus dorsalis) for the autochthonous

 

 

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muscles of the back developing^- from the dorsal part of the myotome and the skin covering it;

(2)   the anterior, ventral branch (ramus ventralis) for the ventral wall of the trun'. and the limbs, developing from the ventral parts of the myo­tonies.

Besides this, another two kinds of branches arise from the cerebro­spinal nerve:

(3)   the communicating branches (rami communicantes) to the sym­pathetic trunk for innervating the internal organs;

(4)   the meningeal branch (ramus meningeus) passing back through the intervertebral orifice for innervating the membranes of the spinal cord.

THE POSTERIOR BRANCHES OF THE SPINAL NERVES

The posterior branches (rami dorsales) of all the cerebrospinal nerves pass backward between the transverse processes of the vertebrae, curving around their articular processes. With the exception of the first cervical, fourth and fifth sacral and coccygeal branches, they all divide into the medial branch (ramus medialis) and lateral branch (ramus lateralis) which supply the skin of the back of the head, the posterior surface of the neck j and back and the deep dorsal muscles.

The posterior branch of the first cervical nerve, n. suboccipitalis emerges between the occipital bone and the atlas and then divides into  branches supplying mm. recti capitis major and minor, m. semispinalis capitis, mm. obiiqui capitis. N. suboccipitalis does not give off branches to the skin. The posterior branch of the second cervical nerve, the greater occipital nerve (n. occipitalis major) coming out between the posterior arch

of the atlas and the second vertebra, pierces the muscles and, having become subcutaneous, innervates the occipital part of the head.

Rami dorsales of the thoracic nerves divide into medial and lateral branches giving rise to branches running to the autochthonous muscles; the skin branches of the superior thoracic nerves originate only from rami mediales, while those of the inferior thoracic nerves, from rami laterales.

The cutaneous branches of the three upper lumbar nerves pass to the superior part of the gluteal region under the name of gluteal branches (of the posterior primary rami of lumbar nerves) (nn. clunium superiores)-, the cutaneous branches of the sacral nerves are called gluteal branches (of the posterior primary rami of sacral nerves) (nn. clunium medii).

THE ANTERIOR BRANCHES OF THE SPINAL NERVES

The anterior branches (rami ventrales) of the spinal nerves innervate the skin and muscles of the ventral wall of the body and both pairs of limbs. Since the skin of the lower abdomen participates in the development of the external sexual organs, the skin covering them is also innervated by the anterior branches. Except for the first two, the anterior branches are much larger than the posterior branches.

The anterior branches of the spinal nerves preserve their original metameric structure only in the thoracic segment (nn. intercostales). In the other segments connected with the limbs in whose development the segmentary character is lost, the nerves arising from the anterior spinal branches intertwine. This is how nervous plexuses are formed in which ex­change of fibres of different neuromeres takes place. A complex redistrib­ution of fibres occurs in the plexuses: the anterior branch of every spinal nerve sends its fibres into several peripheral nerves and, consequently, each of them contains fibres of several segments of the spinal cord. It is therefore understandable that lesion of a nerve arising from the plexus is not attended by disturbed function of all the muscles receiving innervation from the segments which gave origin to this nerve.

Most of the nerves emerging from plexuses are mixed; this is why the clinical picture of the lesion is made up of motor disorders, sensory disorders and vegetative disorders.

Three large plexuses are distinguished: cervical, brachial and lumbo­sacral.

The brachial plexus formed by the ventral rami of spinal nerves C₅-T₁. It lies on the deep neck muscles and is divided into a supraclavicular part and an infraclavicular part.

Supraclavicular Part passes through the interscalenus fora­men and consists of the superior, middle and inferior trunks and gives off motor nerves to the muscles of the shoulder girdle:

·        the dorsal scapular nerve (which supplies the levator scapulae muscle and the rhomboideus major and minor muscles),

·        the suprascapular nerve (supraspinatous muscle and infraspinatous muscle)

·        the subscapular nerve (passes to the subscapular and teres major muscle)

·        the subclavius nerve (to the subclavius muscle)

·        lateral and medial pectoral nerves (which supply the pectoralis major and pectoralis minor muscles)

·        the long thoracic nerve (whose branches supplies the serratus anterior muscle)

·        the thoracodorsal nerve (which sup­plies the latissimus dorsi muscle)

·        Axillary nerve branches off from posterior cord of the Infraclavicular Part. It passes deep in the axillary fossa through the quadrilaterum foramen to the back surface of the scapula. It supplies the capsule of the shoulder joint and gives off motor branches for deltoid and teres minor mus­cles. Branch superior lateral brachial cutaneous nerve passes to the skin, which it supplies the skin in the deltoid region.

The right brachial plexus with its short branches, viewed from in front. The Sternomastoid and Trapezius muscles have been completely, the Omohyoid and Subclavius have been partially, removed; a piece has been sawed out of the clavicle; the Pectoralis muscles have been incised and reflected.

Infraclavicular Part. According to relation to the axil­lary artery they distinguish the lateral cord, the medial cord and the posterior cord.

1.   The nerve to the rhomboids (n. dorsalis scapulae) (from Cy) accom­panies the descending branch of a. transversa colli along the medial edge of the shoulder blade. It innervates m. levator scapulae and mm. rhomboidei.

2.   The nerve to the serratus anterior muscle (n. thoracicus longus) (from Cy-Cvii) descends along the external surface of m. serratus anterior, mhich it supplies.

 

3.   The suprascapular nerve in. suprascapularis) (from C_y and C_yi) passes through the incisura scapulae into the fossa supraspinata and to­gether with a. suprascapularis passes under the acromion into the infraspinous fossa. It innervates mm. supra- and infraspinatus and the capsule of the shoulder joint.

4.   The lateral and medial pectoral nerves (nn. pectorales medialis and lateralis) (from Cy-Th1_x) run to m. pectoralis major and minor.

5.                 The nerve to the subclavius muscle (n. subclavius) (C_v) passes to m. subclavius.

6.   Subscapular nerves (nn. subscapulares) (CV-CvIII) ^suPPly m. sub- scapularis, m. teres major and m. latissimus dorsi. The branch running along the axillary edge of the shoulder blade to m. latissimus dorsi is called n. thoracodorsalis.

7.   The circumflex nerve (n. axillaris) (from C_v-C_vi) is the thickest nerve among the short branches of the brachial plexus. It passes together with a. circumfiexa humeri posterior through the foramen quadrilaterum onto the posterior surface of the surgical neck of the humerus and sends branches to mm. deltoideus, teres minor and to the shoulder joint. Along

 

the posterior edge of the deltoid muscle it gives off a cutaneous branch, n. cutaneous brachii lateralis superior, that innervates the skin of the deltoid and the posterolateral region of the upper arm in its upper part.

 

The Branchial Plexus (plexus brachialis) .

—The brachial plexus is formed by the union of the anterior divisions of the lower four cervical nerves and the greater part of the anterior division of the first thoracic nerve; the fourth cervical usually gives a branch to the fifth cervical, and the first thoracic frequently receives one from the second thoracic. The plexus extends from the lower part of the side of the neck to the axilla. The nerves which form it are nearly equal in size, but their mode of communication is subject to some variation. The following is, however, the most constant arrangement. The fifth and sixth cervical unite soon after their exit from the intervertebral foramina to form a trunk. The eighth cervical and first thoracic also unite to form one trunk, while the seventh cervical runs out alone. Three trunks—upper, middle, and lower—are thus formed, and, as they pass beneath the clavicle, each splits into an anterior and a posterior division. The anterior divisions of the upper and middle trunks unite to form a cord, which is situated on the lateral side of the second part of the axillary artery, and is called the lateral cord or fasciculus of the plexus. The anterior division of the lower trunk passes down on the medial side of the axillary artery, and forms the medial cord or fasciculus of the brachial plexus. The posterior divisions of all three trunks unite to form the posterior cord or fasciculus of the plexus, which is situated behind the second portion of the axillary artery.

The right brachial plexus (infraclavicular portion) in the axillary fossa; viewed from below and in front. The Pectoralis major and minor muscles have been in large part removed; their attachments have been reflected.

 

Relations.—In the neck, the brachial plexus lies in the posterior triangle, being covered by the skin, Platysma, and deep fascia; it is crossed by the supraclavicular nerves, the inferior belly of the Omohyoideus, the external jugular vein, and the transverse cervical artery. It emerges between the Scaleni anterior and medius; its upper part lies above the third part of the subclavian artery, while the trunk formed by the union of the eighth cervical and first thoracic is placed behind the artery; the plexus next passes behind the clavicle, the Subclavius, and the transverse scapular vessels, and lies upon the first digitation of the Serratus anterior, and the Subscapularis. In the axilla it is placed lateral to the first portion of the axillary artery; it surrounds the second part of the artery, one cord lying medial to it, one lateral to it, and one behind it; at the lower part of the axilla it gives off its terminal branches to the upper limb.

 

Branches of Communication.—Close to their exit from the intervertebral foramina the fifth and sixth cervical nerves each receive a gray ramus communicans from the middle cervical ganglion of the sympathetic trunk, and the seventh and eighth cervical similar twigs from the inferior ganglion. The first thoracic nerve receives a gray ramus from, and contributes a white ramus to, the first thoracic ganglion. On the Scalenus anterior the phrenic nerve is joined by a branch from the fifth cervical.

 Branches of Distribution.—The branches of distribution of the brachial plexus may be arranged into two groups, viz., those given off above and those below the clavicle.

 Supraclavicular Branches.

 

 

   The Dorsal Scapular Nerve (n. dorsalis scapulæ; nerve to the Rhomboidei; posterior scapular nerve) arises from the fifth cervical, pierces the Scalenus medius, passes beneath the Levator scapulæ, to which it occasionally gives a twig, and ends in the Rhomboidei.

  The Suprascapular (n. suprascapularis)  arises from the trunk formed by the union of the fifth and sixth cervical nerves. It runs lateralward beneath the Trapezius and the Omohyoideus, and enters the supraspinatous fossa through the suprascapular notch, below, the superior transverse scapular ligament; it then passes beneath the Supraspinatus, and curves around the lateral border of the spine of the scapula to the infraspinatous fossa. In the supraspinatous fossa it gives off two branches to the Supraspinatus muscle, and an articular filament to the shoulder-joint; and in the infraspinatous fossa it gives off two branches to the Infraspinatous muscle, besides some filaments to the shoulder-joint and scapula.

  The Nerve to the Subclavius (n. subclavius) is a small filament, which arises from the point of junction of the fifth and sixth cervical nerves; it descends to the muscle in front of the third part of the subclavian artery and the lower trunk of the plexus, and is usually connected by a filament with the phrenic nerve.

Suprascapular and axillary nerves of right side, seen from behind. (Testut.)

 

 

  The Long Thoracic Nerve (n. thoracalis longus; external respiratory nerve of Bell; posterior thoracic nerve)  supplies the Serratus anterior. It usually arises by three roots from the fifth, sixth, and seventh cervical nerves; but the root from the seventh nerve may be absent. The roots from the fifth and sixth nerves pierce the Scalenus medius, while that from the seventh passes in front of the muscle. The nerve descends behind the brachial plexus and the axillary vessels, resting on the outer surface of the Serratus anterior. It extends along the side of the thorax to the lower border of that muscle, supplying filaments to each of its digitations.

  The branches for the Longus colli and Scaleni arise from the lower four cervical nerves at their exit from the intervertebral foramina.

 

Infraclavicular Branches.—The infraclavicular branches are derived from the three cords of the brachial plexus, but the fasciculi of the nerves may be traced through the plexus to the spinal nerves from which they originate. They are as follows:

 

  The Anterior Thoracic Nerves (nn. thoracales anteriores)  supply the Pectorales major and minor.

  The lateral anterior thoracic (fasciculus lateralis) the larger of the two, arises from the lateral cord of the brachial plexus, and through it from the fifth, sixth, and seventh cervical nerves. It passes across the axillary artery and vein, pierces the coracoclavicular fascia, and is distributed to the deep surface of the Pectoralis major. It sends a filament to join the medial anterior thoracic and form with it a loop in front of the first part of the axillary artery.

  The medial anterior thoracic (fasciculus medialis) arises from the medial cord of the plexus and through it from the eighth cervical and first thoracic. It passes behind the first part of the axillary artery, curves forward between the axillary artery and vein, and unites in front of the artery with a filament from the lateral nerve. It then enters the deep surface of the Pectoralis minor, where it divides into a number of branches, which supply the muscle. Two or three branches pierce the muscle and end in the Pectoralis major.

  The Subscapular Nerves (nn. subscapulares), two in number, spring from the posterior cord of the plexus and through it from the fifth and sixth cervical nerves.

  The upper subscapular (short subscapular), the smaller enters the upper part of the Subscapularis, and is frequently represented by two branches.

  The lower subscapular supplies the lower part of the Subscapularis, and ends in the Teres major; the latter muscle is sometimes supplied by a separate branch.

  The Thoracodorsal Nerve (n. thoracodorsalis; middle or long subscapular nerve), a branch of the posterior cord of the plexus, derives its fibers from the fifth, sixth, and seventh cervical nerves; it follows the course of the subscapular artery, along the posterior wall of the axilla to the Latissimus dorsi, in which it may be traced as far as the lower border of the muscle.

   The Axillary Nerve (n. axillaris; circumflex nerve)  arises from the posterior cord of the brachial plexus, and its fibers are derived from the fifth and sixth cervical nerves. It lies at first behind the axillary artery, and in front of the Subscapularis, and passes downward to the lower border of that muscle. It then winds backward, in company with the posterior humeral circumflex artery, through a quadrilateral space bounded above by the Subscapularis, below by the Teres major, medially by the long head of the Triceps brachii, and laterally by the surgical neck of the humerus, and divides into an anterior and a posterior branch.

  The anterior branch (upper branch) winds around the surgical neck of the humerus, beneath the Deltoideus, with the posterior humeral circumflex vessels, as far as the anterior border of that muscle, supplying it, and giving off a few small cutaneous branches, which pierce the muscle and ramify in the skin covering its lower part.

  The posterior branch (lower branch) supplies the Teres minor and the posterior part of the Deltoideus; upon the branch to the Teres minor an oval enlargement (pseudoganglion) usually exists. The posterior branch then pierces the deep fascia and is continued as the lateral brachial cutaneous nerve, which sweeps around the posterior border of the Deltoideus and supplies the skin over the lower two-thirds of the posterior part of this muscle, as well as that covering the long head of the Triceps brachii .

  The trunk of the axillary nerve gives off an articular filament which enters the shoulder-joint below the subscapularis.

 

Theme 2. Long branches of brachial plexus, topography and distribution of branches on arm, forearm and hand

The long branches:

Among the long branches (Fig. 140) we can distinguish the anterior branches for the flexors and pronators (nn. musculocutaneus, medianus and ulnaris) and the posterior branches for the extensors and supinators (n. radialis).

1.   The musculocutaneous nerve (n. musculocutaneus) originates from the lateral trunk of the brachial plexus (from Cy-CyII), pierces m. cora- cobrachialis and innervates all the anterior muscles of the shoulder: mm. coracobrachialis, biceps and brachialis. On passing between the latter two onto the lateral side of the upper arm, it continues onto the forearm as the lateral cutaneous nerve of the forearm (n. cutaneus antebrachii lateralis) sup­plying the skin of the radial side of the latter and the skin of the thenar.

2.   The median nerve (n. medianus) [Cy-Cvii. Th1), arises from the medial and lateral trunks in two roots which embrace the a. axillaris in

 

front, It then passes into tlie sulcus bicipitalis medialis together with the brachial artery. In the cubital fossa the nerve runs under the m. pronator teres and the superficial flexor of the fingers and then between the latter and the m. flexor digitorum profundus and into the sulcus medianus in the middle of the forearm and to the palm. On the upper arm, the median nerve gives off no branches. On the forearm it gives off rami musculares to all the muscles of the anterior flexor group, with the exception of the m. flexor carpi ulnaris and the part of the deep flexor of the fingers nearest to it (Figs. 141 and 144).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

One of the branches, the posterior interosseous nerve (n. interosseus Iantebrachii] anterior) accompanies the a. interossea anterior on the interos­seous membrane and innervates the deep flexor muscles (m. flexor pollicis longus and part of the flexor digitorum profundus), m. pronator quadratus and the radiocarpal joint. The median nerve gives off a thin cutaneous branch, the palmar cutaneous branch (of the median nerve) (ramus palmaris n. mediani) over the radiocarpal joint. This branch supplies a small area of skin on the thenar and the palm. The median nerve passes onto the palm through the canalis carpi together with the tendons of the flexors and divides into three branches, the common plantar digital nerves (nn. digitales palmares com­munes) which run along the first, second and third metacarpal spaces under the palmar aponeurosis toward the fingers. The first branch innervates the mus­cles of the thenar with the exception of the m. adductor pollicis and the deep head of the m. flexor pollicis brevis which are innervated by the ulnar nerve. The common palmar digital nerves, in turn, divide into seven proper palmar digital nerves (nn. digitales palmares proprii) which pass to both sides of the thumb, to the index and middle fingers and to the radial side of the ring finger. The same branches also supply the skin on the radial side of the palm (Fig. 142); the digital nerves also supply the first and second vermiform muscles.

3.    The ulnar nerve (n. ulnaris) (Figs. 141 and 142) which emerges from the medial trunk of the brachial plexus (CVii> Cviii> Th_x) passes on the medial side of the upper arm to the posterior surface of the medial epicondyle (it lies under the skin here and this is why it gets hurt so often, causing a prickling sensation in the middle zone of the forearm) and then extends in the sulcus ulnaris and further in the canalis carpi ulnaris where it runs, together with the arteries and veins of the same name, to the palm. On the surface of the retinaculum flexorum it transforms into its terminal branch—the ramus palmaris n. ulnaris. Like the median nerve, the ulnar nerve does not give rise to any branches on the upper arm.

The branches of the ulnar nerve on the forearm and hand:

Rami articulares to the ulnar joint.

Rami musculares for the m. flexor carpi ulnaris and its neighbouring portion of the m. flexor digitorum profundus.

Ramus cutaneus palmaris to the skin of the hypothenar.

Ramus dorsalis n. ulnaris emerges through the space between the m. flexor carpi ulnaris and the ulnar bone to reach the dorsal surface of the hand where it divides into five dorsal digital branches, nn. digitales dorsales, for the little and ring fingers and the ulnar side of the middle finger.

Ramus palmaris n. ulnaris, the terminal branch of the ulnar nerve, at the level of the os pisiforme divides into the superficial and deep branches, of which the superficial (ramus superficialis) supplies, via a small muscle branch, the m. palmaris brevis and then the skin on the ulnar side of the palm and, on dividing, gives off three nn. digitales palmares proprii to both sides of the little finger and to the ulnar side of the ring finger.

Ramus profundus, the deep branch of the ulnar nerve, together with the deep branch of the a. ulnaris passes through the space between the m.

 

flexor and m. abductor digiti minimi and accompanies the deep palmar arch. There it innervates all the muscles of hypothenar, all mm. interossei, the third and fourth mm. lumbricales, and from the muscles of the thenar—m. adductor pollicis and the deep head of the m. flexor pollicis brevis. Ramus profundus ends in a thin anastomosis with n. medianus (Fig. 141).

4.   The medial cutaneous nerve of the arm (n. cutaneus brachii medialis) arises from the medial trunk of the plexus (from Cviii, Thj) and passes along the axilla medially to the a. axillaris; it usually joins with the perfo­rating branch of the second thoracic nerve (n. intercostobrachialis), and supplies the skin on the medial surface of the upper arm up to the ulnar joint.

5.   The medial cutaneous nerve of the forearm (n. cutaneus antebrachii medialis) also arises from the medial trunk of the plexus (from Cym, Thi) and lies in the axilla next to the ulnar nerve; in the upper part of the upper

 

arm it is located medially of the brachial artery next to v. basilica together with which it pierces the fascia and becomes subcutaneous. This nerve innervates the’skin on the ulnar (medial) side of the forearm down to the articulations of the hand.

 

       The ulnar nerve passes in the ulnar sulcus on the forearm through the flexor carpi ulnaris muscle and then runs below this muscle to the wrist joint. It does not traverse the carpal tunnel but passes over the flexor retinaculum to the palmar surface of the hand where it divides into superficial and deep branches. In the forearm it gives off branches to the flexor carpi ulnaris muscle and to the ulnar half of the flexor digitorum profundus muscle. In the middle of the forearm a sensory branch is given off, the dorsal branch of the ulnar nerve, which passes to the ulnar side of the back of the hand where it supplies the skin. Another sensory branch, the palmar branch of the ulnar nerve, is given off in the distal third of the forearm. It passes to the palm of the hand and supplies the skin of the hypothenar eminence. The superficial branch, as the fourth com­mon palmar digital nerve, passes to the interosseous space between the ring and little fingers and divides into the proper palmar digital nerves, which supply the sensory innervation of the volar surface of the little finger and the ulnar side of 4-th finger. The deep branch gives off branches to all the muscles of the hypothenar eminence (abductor muscle of the fifth finger, the flexor brevis muscle of the minimus finger, and the opponens muscle of the minimus finger) and all the dorsal and palmar interosseous muscles, the third and fourth lumbrical muscles, the adductor pollicis muscle, and the deep head of the flexor pollicis brevis muscle.

 

1.     Median nerve is formed on the anterior surface of the axillary artery by parts of the medial and lateral cords. The nerve runs to the elbow in the medial bicipital sulcus and does not (!) supply anything in brachial region. Then it reaches the forearm between the two heads of the pronator teres muscle. It extends to the wrist between the flexor digitorum superficialis and the flexor digitorum profundusin median sulcus. Before it enters the carpal canal it lies superficially be­tween the tendons of the flexor carpi radialis muscle and the palmaris longus. In the carpal canal it divides into its terminal branches. The muscular branches of the nerve supply the pronators and most of the flexors of the forearm: pronator teres, the flexor carpi radialis, the palmaris longus and the flexor digitorum superficialis muscle. The anterior antebrachial interosseous nerve runs on the interosseous mem­brane to the deep muscles. In the lower third of the forearm, the sensory palmar branch of the median nerve passes to the skin of the ball of the thumb, the radial side of the wrist and the palm of the hand. The median nerve gives off branches to the periosteum, the elbow joint, the radiocarpal joint and the mediocarpal joint. After passing through the carpal canal the median nerve divides into the common palmar digital nerves I, II, III, each of which divide at the level of the proximal metacarpophalangeal joints into the two proper palmar digital nerves. They give off a branch to the thenar muscles (abduc­tor pollicis brevis muscle, superfi­cial head of the flexor pollicis brevis muscle and the opponens pollicis muscle). The common palmar digital nerves supply the I-II lumbrical muscles. Sensory branches supply the skin of thenar, of the 1^st,  2^d, 3^d and part of the 4^th fingers.

 

             Carpal Tunnel Syndrome

Carpal tunnel syndrome is a condition that causes a "needles-and- pins" sensation to the index and middle finger of the wrist, and is caused by compression or stretching of the medial nerve. It is a common disorder with people whose occupation require a great deal of wrist flexion or prolonged extension. It has been commonly called the "secretary's disease" and is seen commonly in writers, typists, pianists, and even more recently, computer professions. The symptoms can vary, but usually include pain in the middle area of the wrist, swelling of wrist, numbness or tingling in index and middle fingers, and loss of function of hand in severe cases. Splints applied to dorsiflex the wrist occasionally help. Cortisone injections may help, and surgery to strip away build-up of adhesive tissue may be required. This condition can recur even after treatment and tends to worsen in the evening and night.

Cutaneous nerves of right upper extremity. Anterior view.

 

 

Beside the Median nerve Musculocutaneous nerve also start from the lateral cord. The nerve runs through the coraco-brachialis muscle between the biceps and brachialis muscles (and nerve supplies them) as far as the elbow. The sensory fibers of the nerve at the elbow pass through the fascia onto the surface and, as the lateral antebrachial cutaneous nerve, supply the skin in the lateral part of the forearm.

 

The posterior cord gives off the axillary and radial nerves.

Radial nerve runs from the axilla in the radial canal and supplies the long, lateral and medial heads of the triceps brachii and anconaeus mus­cles. Also inferior lateral and posterior brachial cutaneous nerves pass to the skin, which it supplies on the lateral and posterior surface of the arm. Radial nerve crosses the elbow joint and di­vides at the level of the head of the radius into its two terminal branches, the superficial and deep branch. The deep branch gives off numerous muscular branches and fi­nally extends to the wrist joint as the posterior antebrachial interosseous nerve. Radial nerve supplies all superficial and deep posterior antebrachial mus­cles, brachioradialis mus­cles, also skin in posterior region. On the back of the hand the superficial branch gives off the 5 dorsal digital nerves which supply the only skin of radial part of the hand, the back surface of the 1^st, 2^nd, 3^d fingers.

 

Diagram of segmental distribution of the cutaneous nerves of the right upper extremity. Anterior view.

 

 

  The Musculocutaneous Nerve (n. musculocutaneus)  arises from the lateral cord of the brachial plexus, opposite the lower border of the Pectoralis minor, its fibers being derived from the fifth, sixth, and seventh cervical nerves. It pierces the Coracobrachialis muscle and passes obliquely between the Biceps brachii and the Brachialis, to the lateral side of the arm; a little above the elbow it pierces the deep fascia lateral to the tendon of the Biceps brachii and is continued into the forearm as the lateral antibrachial cutaneous nerve. In its course through the arm it supplies the Coracobrachialis, Biceps brachii, and the greater part of the Brachialis. The branch to the Coracobrachialis is given off from the nerve close to its origin, and in some instances as a separate filament from the lateral cord of the plexus; it is derived from the seventh, cervical nerve. The branches to the Biceps brachii and Brachialis are given off after the musculocutaneous has pierced the Coracobrachialis; that supplying the Brachialis gives a filament to the elbow-joint. The nerve also sends a small branch to the bone, which enters the nutrient foramen with the accompanying artery.

Cutaneous nerves of right upper extremity. Posterior view.

 

Diagram of segmental distribution of the cutaneous nerves of the right upper extremity. Posterior view.

 

  The lateral antibrachial cutaneous nerve (n. cutaneus antibrachii cutaneous lateralis; branch of musculocutaneous nerve) passes behind the cephalic vein, and divides, opposite the elbow-joint, into a volar and a dorsal branch.

  The volar branch (ramus volaris; anterior branch) descends along the radial border of the forearm to the wrist, and supplies the skin over the lateral half of its volar surface. At the wrist-joint it is placed in front of the radial artery, and some filaments, piercing the deep fascia, accompany that vessel to the dorsal surface of the carpus. The nerve then passes downward to the ball of the thumb, where it ends in cutaneous filaments. It communicates with the superficial branch of the radial nerve, and with the palmar cutaneous branch of the median nerve.

  The dorsal branch (ramus dorsalis; posterior branch) descends, along the dorsal surface of the radial side of the forearm to the wrist. It supplies the skin of the lower two-thirds of the dorso-lateral surface of the forearm, communicating with the superficial branch of the radial nerve and the dorsal antibrachial cutaneous branch of the radial.

  The musculocutaneous nerve presents frequent irregularities. It may adhere for some distance to the median and then pass outward, beneath the Biceps brachii, instead of through the Coracobrachialis. Some of the fibers of the median may run for some distance in the musculocutaneous and then leave it to join their proper trunk; less frequently the reverse is the case, and the median sends a branch to join the musculocutaneous. The nerve may pass under the Coracobrachialis or through the Biceps brachii. Occasionally it gives a filament to the Pronator teres, and it supplies the dorsal surface of the thumb when the superficial branch of the radial nerve is absent.

  The Medial Antibrachial Cutaneous Nerve (n. cutaneus antibrachii medialis; internal cutaneous nerve arises from the medial cord of the brachial plexus. It derives its fibers from the eighth cervical and first thoracic nerves, and at its commencement is placed medial to the axillary artery. It gives off, near the axilla, a filament, which pierces the fascia and supplies the integument covering the Biceps brachii, nearly as far as the elbow. The nerve then runs down the ulnar side of the arm medial to the brachial artery, pierces the deep fascia with the basilic vein, about the middle of the arm, and divides into a volar and an ulnar branch.

  The volar branch (ramus volaris; anterior branch), the larger, passes usually in front of, but occasionally behind, the vena mediana cubiti (median basilic vein). It then descends on the front of the ulnar side of the forearm, distributing filaments to the skin as far as the wrist, and communicating with the palmar cutaneous branch of the ulnar nerve.

  The ulnar branch (ramus ulnaris; posterior branch) passes obliquely downward on the medial side of the basilic vein, in front of the medial epicondyle of the humerus, to the back of the forearm, and descends on its ulnar side as far as the wrist, distributing filaments to the skin. It communicates with the medial brachial cutaneous, the dorsal antibrachial cutaneous branch of the radial, and the dorsal branch of the ulnar .

  The Medial Brachial Cutaneous Nerve (n. cutaneus brachii medialis; lesser internal cutaneous nerve; nerve of Wrisberg) is distributed to the skin on the ulnar side of the arm. It is the smallest branch of the brachial plexus, and arising from the medial cord receives its fibers from the eighth cervical and first thoracic nerves. It passes through the axilla, at first lying behind, and then medial to the axillary vein, and communicates with the intercostobrachial nerve. It descends along the medial side of the brachial artery to the middle of the arm, where it pierces the deep fascia, and is distributed to the skin of the back of the lower third of the arm, extending as far as the elbow, where some filaments are lost in the skin in front of the medial epicondyle, and others over the olecranon. It communicates with the ulnar branch of the medial antibrachial cutaneous nerve.

  In some cases the medial brachial cutaneous and intercostobrachial are connected by two or three filaments, which form a plexus in the axilla. In other cases the intercostobrachial is of large size, and takes the place of the medial brachial cutaneous, receiving merely a filament of communication from the brachial plexus, which represents the latter nerve; in a few cases, this filament is wanting.

  The Median Nerve (n. medianus) extends along the middle of the arm and forearm to the hand. It arises by two roots, one from the lateral and one from the medial cord of the brachial plexus; these embrace the lower part of the axillary artery, uniting either in front of or lateral to that vessel. Its fibers are derived from the sixth, seventh, and eighth cervical and first thoracic nerves. As it descends through the arm, it lies at first lateral to the brachial artery; about the level of the insertion of the Coracobrachialis it crosses the artery, usually in front of, but occasionally behind it, and lies on its medial side at the bend of the elbow, where it is situated behind the lacertus fibrosus (bicipital fascia), and is separated from the elbow-joint by the Brachialis. In the forearm it passes between the two heads of the Pronator teres and crosses the ulnar artery, but is separated from this vessel by the deep head of the Pronator teres. It descends beneath the Flexor digitorum sublimis, lying on the Flexor digitorum profundus, to within 5 cm. of the transverse carpal ligament; here it becomes more superficial, and is situated between the tendons of the Flexor digitorum sublimis and Flexor carpi radialis. In this situation it lies behind, and rather to the radial side of, the tendon of the Palmaris longus, and is covered by the skin and fascia. It then passes behind the transverse carpal ligament into the palm of the hand. In its course through the forearm it is accompanied by the median artery, a branch of the volar interroseous artery.

 

Branches.—With the exception of the nerve to the Pronator teres, which sometimes arises above the elbow-joint, the median nerve gives off no branches in the arm. As it passes in front of the elbow, it supplies one or two twigs to the joint.

  In the forearm its branches are: muscular, volar interosseous, and palmar.

  The muscular branches (rami musculares) are derived from the nerve near the elbow and supply all the superficial muscles on the front of the forearm, except the Flexor carpi ulnaris.

  The volar interosseous nerve (n. interosseus [antibrachii] volaris; anterior interosseous nerve) supplies the deep muscles on the front of the forearm, except the ulnar half of the Flexor digitorum profundus. It accompanies the volar interosseous artery along the front of the interosseous membrane, in the interval between the Flexor pollicis longus and Flexor digitorum profundus, supplying the whole of the former and the radial half of the latter, and ending below in the Pronator quadratus and wrist-joint.

  The palmar branch (ramus cutaneus palmaris n. mediani) of the median nerve arises at the lower part of the forearm. It pierces the volar carpal ligament, and divides into a lateral and a medial branch; the lateral branch supplies the skin over the ball of the thumb, and communicates with the volar branch of the lateral antibrachial cutaneous nerve; the medial branch supplies the skin of the palm and communicates with the palmar cutaneous branch of the ulnar.

  In the palm of the hand the median nerve is covered by the skin and the palmar aponeurosis, and rests on the tendons of the Flexor muscles. Immediately after emerging from under the transverse carpal ligament the nerve becomes enlarged and flattened and splits into a smaller, lateral, and a larger, medial portion. The lateral portion supplies a short, stout branch to certain of the muscles of the ball of the thumb, viz., the Abductor brevis, the Opponens, and the superficial head of the Flexor brevis, and then divides into three proper volar digital nerves; two of these supply the sides of the thumb, while the third gives a twig to the first Lumbricalis and is distributed to the radial side of the index finger. The medial portion of the nerve divides into two common volar digital nerves. The first of these gives a twig to the second Lumbricalis and runs toward the cleft between the index and middle fingers, where it divides into two proper digital nerves for the adjoining sides of these digits; the second runs toward the cleft between the middle and ring fingers, and splits into two proper digital nerves for the adjoining sides of these digits; it communicates with a branch from the ulnar nerve and sometimes sends a twig to the third Lumbricalis.

  Each proper digital nerve, opposite the base of the first phalanx, gives off a dorsal branch which joins the dorsal digital nerve from the superficial branch of the radial nerve, and supplies the integument on the dorsal aspect of the last phalanx. At the end of the digit, the proper digital nerve divides into two branches, one of which supplies the pulp of the finger, the other ramifies around and beneath the nail. The proper digital nerves, as they run along the fingers, are placed superficial to the corresponding arteries.

Nerves of the left upper extremity.

 

The Ulnar Nerve (n. ulnaris) is placed along the medial side of the limb, and is distributed to the muscles and skin of the forearm and hand. It arises from the medial cord of the brachial plexus, and derives its fibers from the eighth cervical and first thoracic nerves. It is smaller than the median, and lies at first behind it, but diverges from it in its course down the arm. At its origin it lies medial to the axillary artery, and bears the same relation to the brachial artery as far as the middle of the arm. Here it pierces the medial intermuscular septum, runs obliquely across the medial head of the Triceps brachii, and descends to the groove between the medial epicondyle and the olecranon, accompanied by the superior ulnar collateral artery. At the elbow, it rests upon the back of the medial epicondyle, and enters the forearm between the two heads of the Flexor carpi ulnaris. In the forearm, it descends along the ulnar side lying upon the Flexor digitorum profundus; its upper half is covered by the Flexor carpi ulnaris, its lower half lies on the lateral side of the muscle, covered by the integument and fascia. In the upper third of the forearm, it is separated from the ulnar artery by a considerable interval, but in the rest of its extent lies close to the medial side of the artery. About 5 cm. above the wrist it ends by dividing into a dorsal and a volar branch.

 

 

 

 

 

 

 

 

 

 

 

Deep palmar nerves.

 

  The branches of the ulnar nerve are: articular to the elbow-joint, muscular, palmar cutaneous, dorsal, and volar.

  The articular branches to the elbow-joint are several small filaments which arise from the nerve as it lies in the groove between the medial epicondyle and olecranon.

  The muscular branches (rami musculares) two in number, arise near the elbow: one supplies the Flexor carpi ulnaris; the other, the ulnar half of the Flexor digitorum profundus.

  The palmar cutaneous branch (ramus cutaneus palmaris) arises about the middle of the forearm, and descends on the ulnar artery, giving off some filaments to the vessel. It perforates the volar carpal ligament and ends in the skin of the palm, communicating with the palmar branch of the median nerve.

  The dorsal branch (ramus dorsalis manus) arises about 5 cm. above the wrist; it passes backward beneath the Flexor carpi ulnaris, perforates the deep fascia, and, running along the ulnar side of the back of the wrist and hand, divides into two dorsal digital branches; one supplies the ulnar side of the little finger; the other, the adjacent sides of the little and ring fingers. It also sends a twig to join that given by the superficial branch of the radial nerve for the adjoining sides of the middle and ring fingers, and assists in supplying them. A branch is distributed to the metacarpal region of the hand, communicating with a twig of the superficial branch of the radial nerve .

 

 

 

 

The suprascapular, axillary, and radial nerves.

 

  On the little finger the dorsal digital branches extend only as far as the base of the terminal phalanx, and on the ring finger as far as the base of the second phalanx; the more distal parts of these digits are supplied by dorsal branches derived from the proper volar digital branches of the ulnar nerve.

  The volar branch (ramus volaris manus) crosses the transverse carpal ligament on the lateral side of the pisiform bone, medial to and a little behind the ulnar artery. It ends by dividing into a superficial and a deep branch.

  The superficial branch (ramus superficialis [n. ulnaris] supplies the Palmaris brevis, and the skin on the ulnar side of the hand, and divides into a proper volar digital branch for the ulnar side of the little finger, and a common volar digital branch which gives a communicating twig to the median nerve and divides into two proper digital nerves for the adjoining sides of the little and ring fingers . The proper digital branches are distributed to the fingers in the same manner as those of the median.

  The deep branch (ramus profundus) accompanied by the deep branch of the ulnar artery, passes between the Abductor digiti quinti and Flexor digiti quinti brevis; it then perforates the Opponens digiti quinti and follows the course of the deep volar arch beneath the Flexor tendons. At its origin it supplies the three short muscles of the little finger. As it crosses the deep part of the hand, it supplies all the Interossei and the third and fourth Lumbricales; it ends by supplying the Adductores pollicis and the medial head of the Flexor pollicis brevis. It also sends articular filaments to the wrist-joint.

  It has been pointed out that the ulnar part of the Flexor digitorum profundus is supplied by the ulnar nerve; the third and fourth Lumbricales, which are connected with the tendons of this part of the muscle, are supplied by the same nerve. In like manner the lateral part of the Flexor digitorum profundus and the first and second Lumbricales are supplied by the median nerve; the third Lumbricalis frequently receives an additional twig from the median nerve.

  The Radial Nerve (n. radialis; musculospiral nerve)  the largest branch of the brachial plexus, is the continuation of the posterior cord of the plexus. Its fibres are derived from the fifth, sixth, seventh, and eighth cervical and first thoracic nerves. It descends behind the first part of the axillary artery and the upper part of the brachial artery, and in front of the tendons of the Latissimus dorsi and Teres major. It then winds around from the medial to the lateral side of the humerus in a groove with the a. profunda brachii, between the medial and lateral heads of the Triceps brachii. It pierces the lateral intermuscular septum, and passes between the Brachialis and Brachioradialis to the front of the lateral epicondyle, where it divides into a superficial and a deep branch.

The branches of the musculospiral nerve are:

Muscular.

Superficial.

Cutaneous.

Deep.

  The muscular branches (rami musculares) supply the Triceps brachii, Anconæus, Brachioradialis, Extensor carpi radialis longus, and Brachialis, and are grouped as medial, posterior, and lateral.

  The medial muscular branches supply the medial and long heads of the Triceps brachii. That to the medial head is a long, slender filament, which lies close to the ulnar nerve as far as the lower third of the arm, and is therefore frequently spoken of as the ulnar collateral nerve.

  The posterior muscular branch, of large size, arises from the nerve in the groove between the Triceps brachii and the humerus. It divides into filaments, which supply the medial and lateral heads of the Triceps brachii and the Anconæus muscles. The branch for the latter muscle is a long, slender filament, which descends in the substance of the medial head of the Triceps brachii.

  The lateral muscular branches supply the Brachioradialis, Extensor carpi radialis longus, and the lateral part of the Brachialis.

  The cutaneous branches are two in number, the posterior brachial cutaneous and the dorsal antibrachial cutaneous.

  The posterior brachial cutaneous nerve (n. cutaneus brachii posterior; internal cutaneous branch of musculospiral) arises in the axilla, with the medial muscular branch. It is of small size, and passes through the axilla to the medial side of the area supplying the skin on its dorsal surface nearly as far as the olecranon. In its course it crosses behind, and communicates with, the intercostobrachial.

  The dorsal antibrachial cutaneous nerve (n. cutaneus antibrachii dorsalis; external cutaneous branch of musculospiral) perforates the lateral head of the Triceps brachii at its attachment to the humerus. The upper and smaller branch of the nerve passes to the front of the elbow, lying close to the cephalic vein, and supplies the skin of the lower half of the arm. The lower branch pierces the deep fascia below the insertion of the Deltoideus, and descends along the lateral side of the arm and elbow, and then along the back of the forearm to the wrist, supplying the skin in its course, and joining, near its termination, with the dorsal branch of the lateral antibrachial cutaneous nerve.

  The Superficial Branch of the Radial Nerve (ramus superficialis radial nerve) passes along the front of the radial side of the forearm to the commencement of its lower third. It lies at first slightly lateral to the radial artery, concealed beneath the Brachioradialis. In the middle third of the forearm, it lies behind the same muscle, close to the lateral side of the artery. It quits the artery about 7 cm. above the wrist, passes beneath the tendon of the Brachioradialis, and, piercing the deep fascia, divides into two branches.

  The lateral branch, the smaller, supplies the skin of the radial side and ball of the thumb, joining with the volar branch of the lateral antibrachial cutaneous nerve.

  The medial branch communicates, above the wrist, with the dorsal branch of the lateral antibrachial cutaneous, and, on the back of the hand, with the dorsal branch of the ulnar nerve. It then divides into four digital nerves, which are distributed as follows: the first supplies the ulnar side of the thumb; the second, the radial side of the index finger; the third, the adjoining sides of the index and middle fingers; the fourth communicates with a filament from the dorsal branch of the ulnar nerve, and supplies the adjacent sides of the middle and ring fingers.

  The Deep Branch of the Radial Nerve (n. interosseus dorsalis; dorsal or posterior interosseous nerve) winds to the back of the forearm around the lateral side of the radius between the two planes of fibers of the Supinator, and is prolonged downward between the superficial and deep layers of muscles, to the middle of the forearm. Considerably diminished in size, it descends, as the dorsal interosseous nerve, on the interosseous membrane, in front of the Extensor pollicis longus, to the back of the carpus, where it presents a gangliform enlargement from which filaments are distributed to the ligaments and articulations of the carpus. It supplies all the muscles on the radial side and dorsal surface of the forearm, excepting the Anconæus, Brachioradialis, and Extenosr carpi radialis longus.