6. The abducens nerve (Nervus abducens, Ecker and Hoffmann; included in the trigeminal, Wyman), (Figs. 111 and 112 VI). This very slender nerve courses along the inner wall of the cranium from its origin to the Gasserian ganglion (q.v.) which it joins, and leaves this in contact with the ophthalmic division of the trigeminal nerve: the nerve then bifurcates in the orbit; the outer branch supplies the Rectus externus, the inner inosculates with small twigs of the ophthalmic division of the trigeminal, and then gives off a number of small ciliary nerves, already described, and one special branch to the Retractor bulbi.

7. The facial nerve (N. facialis, Ecker and Hoffmann; Facialis (Portio dura), Wyman; Facial or Jugular Nerve, Stannius), (Figs. 111, 113, and 114 Ve VII) arises immediately behind the trigeminal, and runs forwards, first in company with the auditory nerve, then alone, to the Gasserian ganglion (q.v.), with which it unites; it again appears at the posterior angle of the ganglion, and escapes from the cranium in company with, and immediately behind, the Ramus mandibularis of the trigeminal, and divides at once into two branches.

a. The Ramus palatinus at once unites with the palatine branch of the ophthalmic division of the trigeminal nerve. Wiedersheim doubts this arrangement, and holds that the two portions arise in common from the Gasserian ganglion; neither has Wyman (Rana pipiens) described this branch of the facial. [De Watteville states that the Ramus palatinus and the palatine branch of the ophthalmic nerve are separated by the carotid artery. In urodeles the two nerves are distinct.]

b. The Ramus hyomandibularis (Ramus jugularis, Hoffmann; Facial Nerve, Wyman), (Figs. 113 and 114, Ve VII). The nerve is directed outwards and backwards so as to pass around the bony wall of the auditory capsule, it then crosses over the inner end of the columella, with which it is in close contact, and is then joined, under cover of the sterno-cleido-mastoideus (sc), by a branch (Ramus communicans) of the glossopharyngeal (see Fig. 111 *). The single trunk (F) so formed is directed downwards in the posterior wall of the Eustachian tube to just above the angle of the mandible, where it divides into three branches, or sometimes into two, in which case a third nerve is supplied by one of the others, usually by the Ramus hyoideus.

(1) The Ramus mandibularis (Ramus mentalis, Hoffmann; Third Trunk of the Facial, Wyman), (Figs. 114 mt and 115 m′) passes inside the angle of the jaw and courses forwards, between the skin and mylo-hyoid muscle, parallel to the Ramus mandibularis of the trigeminal nerve, as far as the symphysis. It supplies small twigs to the neighbouring parts of the mucous membrane of the mouth.

(2) The Ramus hyoideus (Ramus jugularis, Hoffmann; Second Trunk of the Facial, Wyman), (Figs. 114, 115 h) is the largest division of the facial; it courses forwards subcutaneously over the deltoideus and the hinder fibres of the mylo-hyoideus to the anterior cornu of the hyoid bone, supplying its muscles and the skin of the throat and sternal region.

(3) The Ramus auricularis (First Trunk of the Facial, Wyman); is a small branch, directed outwards; it supplies a branch to the walls of the tympanic cavity, and is finally distributed in the skin under the tympanic membrane and behind the angle of the mouth.

8. The auditory nerve (N. acusticus, Ecker, Hoffmann; Auditory Nerve, Wyman). This nerve has a very short course in the cranium; it reaches the auditory organ by a foramen (Fig. 116 VIII) in the auditory capsule, and is then distributed in the ear, with which it will be described.

9. The glossopharyngeal nerve (N. glosso­pharyngeus, Ecker; Ramus glosso-pharyngeus, Hoffmann; Glosso­pharyngeal, Wyman; Glossopharyngeal of the Vagus, Müller), (Figs. 102 and 103 X, 111, 113, 114, and 115 X²) arises in common with the pneumogastric nerve, and quits the skull with it through an opening (Canalis nervi vagi) immediately behind the auditory capsule, and at once divides into two branches; both of which lie under the MM. in tertransversarii capitis and are covered by the Depressor mandibulae.

a. The Ramus anterior (Verbindungsast des Glossopharyngeus, Wiedersheim; Ramus communicans, Hoffmann; Uniting Branch, Wyman; Laryngeal Branch of the Vagus, Volkmann; Communicans ad facialem, de Watteville), (Figs. 111, 113, and 114 X¹). This nerve curves downwards and forwards around the auditory capsule and beneath the Depressor mandibuli to join the facial nerve, as already described.

b. The Ramus posterior (N. glossopharyngeus, Wiedersheim; Ramus lingualis, Hoffmann), (Figs. 111, 113, and 114 X²). This nerve runs downwards and forwards to the ventral surface of the pharynx, dips underneath the Petrohyoideus IV, to appear again, after a short interval, by piercing the Petrohyoideus II or III, courses parallel to and behind the anterior cornu of the hyoid bone, and thus reaches the floor of the mouth. The nerve then runs forwards in a very sinuous course, close to the median line, and between the Geniohyoideus and Hyoglossus; in its course on the floor of the mouth it crosses the hypoglossal nerve. It supplies the petrohyoid muscles, and gives numerous small branches to the mucous membrane of the pharynx (Ramus pharyngeus, Hoffmann).

10. The pneumogastric or vagus nerve (Vagus; Ramus intestinalis nervi vagi, Fischer, Hoffmann; Vagal Trunk, Wyman; Vaso-sympathetic, Gaskell), (Figs. 111, 113, 114, and 115 X³). This nerve arises in common with the glossopharyngeal; the two nerves leave the skull together by an opening in the exoccipital bone (Canalis nervi vagi); immediately outside the skull they acquire a ganglionic enlargement (Ganglion condyloideum, Ganglion nervi vagi), (Fig. 111 XG); in this course the glossopharyngeal lies in front of the pneumogastric, which it then leaves. The pneumogastric lies first upon the M. levator anguli scapulae, then running backwards and downwards along the hinder border of the Petrohyoideus IV it comes to the side of the pharynx; it is covered by the trapezius, and passes between the hypoglossal nerve and the Aorta ascendens; arriving at the Arteria pulmonalis, it gives off its terminal branches. [Gaskell has proved that this nerve contains both sympathetic and vagal elements, and that it is therefore really a vago-sympathetic.]

The branches and communications of the pneumogastric nerve are:‍—

a. Communications between the ganglion of the pneumogastric and the sympathetic system (Fig. 111 Sp), which again connect it with the Gasserian ganglion of the trigeminal nerve (Fig. 111 VS, Vg); (see sympathetic system).

b. [The Ramus cutaneus dorsalis (Fischer) is considered by Stannius and Fürbringer to be the homologue of the Ramus auricularis; it passes outwards between the digastricus and temporalis to be distributed in the skin of the suprascapular region. This nerve is the persistent portion of the N. lateralis nervi vagi of the tadpole.]

c. During its course over the petrohyoidei the vagus gives off a few twigs (Fig. 114 pp), which form a fine plexus to supply these muscles and the pharynx [also a twig to the trachea, according to Hoffmann].

d. The Ramus accessorius (Fürbringer, Hoffmann, Ecker), (Fig. 114 XI) is usually a single small nerve which runs between the intertransversarii muscles and the trapezius: it supplies the under surface of the latter muscle.

e. The Ramus scapularis (Hoffmann) is a very slender nerve arising near the Ramus accessorius; it passes along the under surface of the trapezius to the inner surface of the interscapularis, which it supplies.

f. The Ramus laryngeus (Recurrens vagi), (Figs. 114 and 115 X3l) runs for some distance parallel to the pneumogastric, separated from it by the petrohyoideus IV; arriving at the hinder cornu of the hyoid bone the nerve loops round the Arteria pulmonalis, and divides into two branches for the supply of the larynx.

g. The Rami gastrici (Fig. 114 X3g) are usually two in number: they pierce the partial diaphragm formed by the anterior fibres of the M. obliquus internus and terminate in the walls of the stomach.

h. The Rami pulmonales (Figs. 114 and 115 X3p) also perforate the partial diaphragm, and then course along the pulmonary arteries to the lungs.

i. The Ramus cardiacus (Figs. 114 and 115 X3c). This nerve is usually smaller on the right side than on the left; it passes along the dorsal surface of the pulmonary artery and Vena cava superior to the Sinus venosus; in this course it gives off two or three twigs to the roots of the lungs: the two nerves communicate just before reaching the heart and pass on to the auricular septum, whence they are distributed to the heart.

j. A slender Laryngeal nerve arises from the vagus alongside the Ramus cardiacus; it courses along the hinder end of the greater cornu of the hyoid to the outer side of the pharynx, which it pierces to pass to the larynx.

F. The Spinal Nerves.

I. General description. Ten pairs of nerves arise, as already described (p. 135), from the spinal cord; each nerve has two roots, a ventral or anterior, and a dorsal or posterior, which unite at their points of exit from the intervertebral foramen: just before, and for a short distance beyond this union, each dorsal root bears a ganglionic enlargement.

a. The length and direction of the various Nerve-roots vary greatly; the roots of the anterior spinal nerves run a very short course, almost transversely outwards, from their points of origin to the intervertebral foramina: the roots of the middle and posterior nerves, in consequence of the vertebral column being considerably longer than that part of the cord belonging to it, pass obliquely backwards to the foramina, the hinder nerves of the Cauda equina running for a considerable distance in the vertebral canal (Fig. 116). The relations of these roots are as follows:‍—

(1) The roots of the first nerve (N. hypoglossus) arise from the spinal cord at a point between the first and second vertebrae; they run transversely outwards to escape between the first and second vertebrae. The dorsal root is extremely slender.

(2) The roots of the second nerve (N. brachialis) arise at the level of the second vertebra and leave the vertebral canal between the second and third vertebrae.

(3) The roots of the third nerve arise from the cord between the second and third vertebrae, and pass out between the third and fourth vertebrae.

(4) The fourth nerve arises by its two roots at the level of the fourth vertebra, and quits the vertebral canal between the fourth and fifth vertebrae.

(5) The fifth nerve arises opposite the fourth vertebra, and passes outwards and slightly backwards to the foramen between the fifth and sixth vertebrae.

(6) The roots of the sixth nerve are attached to the cord opposite the fourth vertebra, and leave the vertebral canal between the sixth and seventh vertebrae.

(7) The seventh nerve arises from the cord at a point between the fourth and fifth vertebrae, and leaves the canal between the seventh and eighth vertebrae.

(8) The eighth nerve quits the cord at a point opposite the articulation between the fifth and sixth vertebrae, then runs backwards to the eighth vertebra, and escapes between this and the ninth vertebra.

(9) The ninth nerve arises at the level of the sixth vertebra, and passes out between the sacrum (ninth vertebra) and the urostyle.

(10) The tenth nerve (N. coccygeus) arises from the cord immediately behind the ninth nerve and opposite the sixth vertebra, and courses alongside the terminal filament to pass out through a foramen in the urostyle (canalis coccygeus).

b. [The Spinal ganglia (Ganglia intervertebralia).

At their exit from the intervertebral foramen the two roots of each nerve unite and bear a ganglionic enlargement, which is in intimate connection with the dorsal root, but is merely in contact with the ventral root. The ganglia lie‍58 in the large intervertebral depressions, upon the under surface of the Proc. obliqui, above and behind, being in relation with the bodies of the vertebrae internally, and the Musculi intertransversarii externally (Fig. 119); ventrally the ganglia are, more or less, covered by the ‘periganglionic glands.’ The ganglia vary much in size; that of the first spinal nerve is the smallest. The ganglion is not attached to the dorsal root alone but is prolonged a short distance beyond the point of union of the two roots; this is best seen in the nerves of the lumbar plexus. Each ganglion is a yellowish-white rounded or oval body, with an outer thick (sometimes 0.15 mm. thick) sheath of connective-tissue, connected by the epineurium of the nerve roots with the Dura mater. This sheath is composed of bundles of parallel, wavy, white, connective-tissue fibres, which enclose a large number of connective-tissue corpuscles, and here and there contains brown pigment.

By means of longitudinal and transverse sections it may be seen that the ganglion surrounds the ventral root, but that it forms a thinner layer on that side, where the dorsal root joins the ventral; although at this point the two roots and the ganglion are firmly united together, the thick fibrous sheath of the ganglion prevents any communication between the nervous elements of the ventral root and those of the ganglion.

The sheath contains nerve-cells and fibres, and sends in a few fine processes to support these structures. The fibres of the posterior root enter and pass out of the ganglion without suffering any changes, except that the nerve fibres are slightly separated by the presence of a few nerve-cells, and that a distinct increase in the number of nerve fibres takes place. The nerve-cells, of which the ganglion is chiefly composed, and upon the number of which its size directly depends, are arranged chiefly around the fibres of the dorsal root; such few as lie between the fibres are smaller than the rest and vary more in their relative numbers; at times one or two isolated cells are found in the capsule or even in the adjoining ‘periganglionic gland.’ The cells near the capsule are somewhat smaller than the deeper cells.‍59 Each of these cells, which are usually pear-shaped, possesses only one process; the cell membrane is thick, resistant, and possessed of an external nucleated, endothelial covering, the space around being probably a pericellular lymph-space; it often contains one to three small fat-globules; the protoplasm of these has, according to v. Lenhossék, a concentric fibrillation; the nucleus is round, clear, and distinct, and relatively larger the smaller the nerve-cell; it is usually placed in the centre of the cell.

In that portion of the cell towards the process is a portion brighter and less easily stained than the rest of the cell (Polarkernen, Courvoisier); this apparently possesses one or two nuclei, and is regarded as a cell by Lenhossék (Polarzellen); the process of each cell soon acquires a medullated sheath, and after a short course, 0.09 mm. to 0.35 mm., divides usually about the third constriction (Lenhossék). These processes all pass peripherally, even those which appear at first to pass in the opposite direction curve round again; it is chiefly due to these fibres that the spinal nerve is larger than its two roots.

In addition to the above, smaller, irregular cells from 5 µ to 7 µ in length are found; Rawitz regards them as young cells, Lenhossék as cells capable of (entwicklungsfähige) developing into nerve-cells. The ganglia contain only few blood-vessels.]

The above description is founded upon that of Lenhossék, and has been confirmed by the translator in every particular, except that only very indistinct and unsatisfactory indications of the concentric fibrillation so clearly delineated by Lenhossék were obtained; the structure of the Gasserian ganglion was found to correspond exactly with the description here given of the structure of the spinal ganglia. The nucleus was oftener at the side than at the centre of the cell.

c. The ‘Periganglionic Glands’ (Periganglionäre Kalkdrüsen, v. Lenhossék; Kalksäckchen, Ecker, and others; Crystal capsules, Wyman; Calcareous Sacs or Masses, of other writers), (Fig. 119). These bodies are found on the ganglia of all the spinal nerves and on the Gasserian ganglion of the trigeminal nerve; they have recently been carefully investigated by v. Lenhossék. According to his description there are usually two to each ganglion, lying on its sides and ventral surface; each consists of a connective-tissue capsule which sends in a few fine trabeculae to support a system of glandular tubes: these usually run parallel to the long axis of the gland, and are about 14 µ to 15 µ in diameter; each tube is lined with a single layer of somewhat columnar epithelium, the cells of which have sharp, distinct outlines and oval nuclei.

A membrana propria was not made out with certainty; the lumen of the tubes is wide and contains a milky fluid, which gives the whole structure its characteristic appearance; it has long been known (Blasius, 1681, mentions the fact, l.c., p. 291) that this fluid contains calcareous matter, which effervesces and dissolves in the presence of hydrochloric acid; the crystals vary in form but are chiefly oval (Wyman).

These glands bear no definite proportion to the size of the nerves to which they are attached (Fig. 118); they already contain calcareous matter during the tadpole stage before the limbs are developed (Stannius, Wyman). No ducts have been traced to these glands. This description, founded upon that of Lenhossék, can be confirmed by the translator in every particular; his sections, however, would lead him to believe that the glands are far more vascular than the description and the drawings of Lenhossék imply.]

d. The Branches of the complete spinal nerves formed by the union of the dorsal and ventral roots with the ganglion (Fig. 120) are usually described as two, a dorsal and a ventral branch, which latter at once gives off a Ramus communicans to the sympathetic system; these two branches are given off almost immediately beyond the ganglion.

II. The Individual Nerves.

A. The Dorsal Branches (Fig. 121).

The dorsal branches are smaller than the ventral; they pass upwards between the inner borders of the Musc. intertransversarii and the articular processes of the vertebrae to reach the under surface of the M. longissimus dorsi; the general course of these nerves is very similar for all; each nerve gives off‍—

(a) A twig to the Musc. intertransversarius and then divides into two branches.

(b) A Ramus muscularis (Fig. 121 rm), which passes outwards to supply the M. longissimus dorsi.

(c) A Ramus cutaneus (Fig. 121 rc); this nerve continues under the extensor muscle of the back, running on the arch of the vertebra towards the middle line; it then pierces the muscle and Fascia dorsalis to reach the large dorsal lymph-sac (Sacc. cranio-dorsalis), through which it courses to end in the skin. In its course through the sac the nerve is connected with a small artery and vein by a small amount of connective-tissue, the whole being enclosed in a sheath of endothelium continuous with that of the general cavity.

The three anterior cutaneous nerves pierce the Fascia dorsalis near the spinous processes, the fourth a little to the side, the fifth perforates the M. coccygeo-iliacus at about the junction of its anterior and middle thirds; the sixth and seventh perforate the same muscle, but more posteriorly. There are seven of these Rami cutanei, the first coming from the second spinal nerve, the rest from the succeeding six spinal nerves.

B. The Ventral Branches.

The ventral branches of the spinal nerves are larger than their corresponding dorsal branches: each nerve gives off immediately a Ramus communicans to the sympathetic system (Figs. 117 SM, 120 C); these Rami communicantes will be described with the sympathetic system; the remaining portions of the ventral divisions of the original spinal nerves are usually known as the spinal nerves; they will be described as such in detail.

1. The hypoglossal nerve‍60 (N. hypoglossus, N. spinalis I), (Figs. 114 115, and 117 M1), or first spinal nerve, is of small size; it leaves the vertebral canal between the first and second vertebrae to lie between the Musculi intertransversarii and the pharynx, where it has in front the Arteria vertebralis, behind the Arteria and Nervus brachialis; passing under the Levator anguli scapulae, it touches the Aorta ascendens and crosses the Vagus and the Carotid-gland, and thus reaches the space between the Musculi sterno-hyoidei and the Petro-hyoideus; then curving forwards sharply it turns under the Mylo-hyoideus to course between the fibres of the Genio-hyoideus to the root of the tongue, where it ends. It first lies to the inner and then to the outer side of the glossopharyngeal nerve. In its course the nerve gives off the following branches:‍—

(a) One or two communicating twigs (Figs. 114 and 122) to the second spinal nerve.

(b) Muscular twigs to the Longissimus dorsi, Intertransversarii capitis, Levator anguli scapulae, and the Retrahens scapulae.

(c) When near the glossopharyngeal it supplies twigs to the Geniohyoideus, Sternohyoideus, and Omohyoideus, where it bifurcates.

(d) One of the branches passes inwards to supply the Hyoglossus.

(e) The other terminal branch passes forwards with the Ramus lingualis and the glossopharyngeal, between the fibres of the Geniohyoideus, which it partially supplies, and sends twigs to the neighbouring parts.

(f) [Hoffmann describes a communicating branch to the pneumogastric nerve, which the translator has not been able to discover, and which no other observer has mentioned.]

2. The second spinal or brachial nerve (N. brachialis, N. spinalis II), (Fig. 122) is a large nerve, leaving the vertebral canal between the second and third vertebrae; it then accompanies the Art. axillaris along the anterior border of the transverse process of the third vertebra, over the hinder end of the Musc. levator scapulae and the anterior end of the m. transverso-scapularis major, to the inner border of the Musc. subscapularis, under which it passes into the arm. In this course it gives off or receives the following branches:‍—

(a) It first receives a branch from the second spinal nerve.

(b) It gives off a large branch, the N. coraco-clavicularis (Fig. 122 Cc), which first accompanies a branch of the Art. axillaris on the Musc. levat. scapulae, then courses forwards and outwards over the Musc. sub­sca­pu­la­ris to pass from above into the Foramen ovale between the clavicle and coracoid bones. It gives off two branches:

(1) One immediately beyond its origin, which runs backwards over the Musc. subscapularis to supply the Musc. obliq. abdominis internus (Fig. 122 Cc′).

(2) While in the Foramen ovale, the N. coraco-clavicularis bifurcates; the anterior twig runs forwards and outwards to the deltoideus and also supplies a recurrent filament to the Musc. sterno-radialis; the posterior twig enters the upper surface of the Musc. stero-radialis.

(c) At the outer extremity of the Musc. transverso-scapularis the brachial nerve gives off a posterior branch, which at once bifurcates:

(1) The first branch passes into the under surface of the Musc. latissimus dorsi (ld), giving a twig to the Infraspinatus.

(2) The second is the Ramus cutaneus axillaris (IIc); it passes on the under surface and posterior border of the Musc. latissimus dorsi to the skin of axilla and dorsal surface of the upper arm.

(d) Several small branches are given off from the upper and anterior surfaces of the brachial nerve near the Foramen ovale; they accompany an artery to pass forwards and upwards between the Musc. subscapularis and the M. transverso-scapularis on the one side, and the long head of the M. triceps brachialis on the other, and are lost in the M. deltoideus and the M. infraspinatus.

The N. brachialis continues its course by passing between the long and inner heads of the M. triceps, reaches the arm and splits into two nerves, the N. ulnaris and the N. radialis.

[I.] The N. ulnaris (Fig. 123 U) escapes from cover of the long head of the M. triceps and runs obliquely over its inner head towards the outer side of the Plica cubiti; in this course it supplies four branches:

α. The Ramus subscapularis passes dorsally to the M. subscapularis.

β. A Ramus pectoralis (Fig. 123 up), passes forwards to the M. abdomino-pectoralis and to the skin of the pectoral region (R. cutaneus pectoralis).

γ. The N. cutaneus antibrachii superior s. medialis (uc) passes to the skin of the inner side of the forearm; this and the two following nerves are given off near the Plica cubiti.

δ. The N. cutaneus antibrachii inferior s. dorsalis s. musculo-cutaneus (uc′) at once supplies branches to the M. flexor carpi radialis‍61, and then runs downwards upon the muscle and bifurcates:‍—

[1] The R. lateralis is distributed, by two twigs, in the M. flexor carpi ulnaris and in the skin of the second finger, to which it supplies the Rami digitales volaris and dorsalis.

[2] The R. dorsalis, after giving a cutaneous twig to the second finger, is distributed by numerous twigs to the skin of the dorsal surface of the hand.

The N. ulnaris then passes between the M. flexor carpi radialis and the tendon of the M. sterno-radialis, sinks deeply into the Plica cubiti, where it lies between the M. flexor carpi radialis and the Flexor carpi ulnaris, then between the latter and the Flexor anti-brachii medialis on the one side and the Flexor digitorum communis on the other: it supplies branches to all these muscles, and while still in the forearm divides into two terminal branches:‍—

α. The R. ulnaris medialis is the smaller; it runs inwards, passes under the tendon of the M. extensor carpi ulnaris into the palm of the hand and ends as the N. volaris digiti V medialis.

β. The R. ulnaris lateralis passes near the thumb-rudiment, covered by the M. abductor pollicis, deeply into the palm of the hand, and supplies by bifurcating branches the adjacent sides of the second, third, fourth, and fifth fingers (R. volares); it also gives twigs to the muscles of the palm.

[II.] The N. radialis (Figs. 123, 124, and 125 R) passes immediately beyond its origin from the N. brachialis, between the humerus and the M. triceps, runs along the bone to its outer side; in this course it gives off:‍—

α. Rami musculares to the separate parts of the M. triceps.

β. The Ramus cutaneus superior (Fig. 125 rc) to the skin of the outer surface of the upper arm and forearm.

The nerve then sinks deeply under the origins of the M. extensor carpi ulnaris and the M. extensor digitorum communis, where it bifurcates after giving off some small twigs:‍—

γ. Small muscular twigs to the extensor muscles of the hand and fingers.

δ. The R. radialis medialis (R2), the smaller terminal branch, supplies a branch to the M. extensor digit. comm. longus and the skin over the carpus (Ramus cutaneus inferior, rc′), and ends on the muscles of the little finger as the R. dorsalis digiti V medialis.

ε. The R. radialis lateralis (R), the larger of the two branches, supplies the extensor muscles of the fingers and gives bifurcating branches, Rami digitales dorsales, to the adjacent sides of the second, third, fourth, and fifth fingers (the Ramus dorsalis lateralis of the second finger is supplied by the N. ulnaris).

3. The third spinal nerve (N. spinalis III) (Fig. 122 SIII) leaves the vertebral canal by the foramen between the third and fourth vertebrae, and runs outwards and forwards upon the large transverse process of the third vertebra to the brachial nerve (N. spinalis II). Its behaviour at this point is subject to considerable variation; at times it joins the brachial nerve completely, at other times the two nerves are simply in contact; or lastly, it may send a small twig to the brachial nerve. Externally to this point the two nerves supply a number of small branches, which may belong almost entirely to either one nerve or the other; these nerves again inosculate in a variable manner, to form an axillary plexus. The more constant branches are:‍—

(1) One or more twigs to the Musc. transverso-scapularis major.

(2) Several branches, usually two larger and one smaller; they course in the M. obliq. abdom. internus (Fig. 122 oi) to the M. rectus, where they give off branches, then pierce the muscle to reach the skin (R. cutaneus abdominalis), (Fig. 122 IIIc).