are at one time iiattened buds coming off at right angles from the side of the body and having dorsal and ventral surfaces, one (preaxial) border toward the head of the embryo, and one (post axial) toward the tail. If a. person lies prone upon the floor with the arms outstretched and the palms downward the embryological position of the forelimb is to some extent restored, and it will now be easily understood that the more preaxial part of the limb will be supplied by those nerves which enter it from nearer the head, while the post axial part draws its nerve supply from lower down the spinal cord. To use Herringham's words: “ (A) Of two spots on the skin, that nearer the preaxial border tends to be supplied by the higher nerve. (B) Of two spots in the preaxial area the lower tends to be supplied by the lower nerve, and of two spots in the post axial area the lower tends to be supplied by the higher nerve.” Other points of general importance in regard to cutaneous nerve supply are, firstly. that the area of skin supplied by one spinal nerve is not sharply marked ofi from that of the next, but the two are separated outer head. of the median nerve (C. 5?, 6, 7), which joins the inner head (C. 8, Th. I) and supplies most of the fiexor muscles of the front of the forearm as well as those of the ball of the thumb, the outer two lumbricals and also the skin of the outer part of the palm including the outer three digits and half the fourth. From the inner cord come the inner head of the median just mentioned, the ulnar nerve (C. 8, Th. I), which passes down behind the internal condyle of the humerus, where it is popularly known as the “funny bone" and supplies the flexor carpi ulnaris, half the flexor rofundus digitorum, and most of the muscles of the hand as well) as the inner digit and a half on the palmar and dorsal aspects. Other branches of the inner cord are the internal cutaneous (C. 8, Th. 1) sup lying the inner side of the forearm, the lesser internal cutaneous (QF h. I) which often joins the intercosto-humeral or lateral cutaneous branch of the second intercostal nerve to supply the skin on the inner side of the upper arm, and the internal anterior °<&s.

thoracic nerve (C. 8, Th. I) to the pectoral is minor and major. From the posterior cord are derived the

three sub scapular nerves (C. 5, 6, 7, 8)

which supply the subscapularis, teres

ma]or and latissimus dorsi muscles, the

V7 ~ s§ v circurrglex nerve (C. 5, 6) supplying the rf 7 deltol and teres minor muscles, and tne A ' W skin over the lower part of the deltoid, / / -'.', //Y f jllr arfqd tlhe musilulaspiral nerve (C. 5, 6, 7, S) " g ' '~ 6;, TA w ic is the 1arge't branch of the »., ' ' brachial plexus and;fives off cutaneous F* 7 r ' twigs to the outer side and back of the I/l, iw/ arm and to the back of the forearm, as well ik ' yi “Q 1,1 as muscular twigs to the triceps and lu. 7 //, ig/, F adjacent musclesx At the elbow this

,     If nerve divides into the radial and posterior

W, ' interosseous. The radial is entirely sen;

 , ., . 'l' sory and supplies the skin of the outer side

, , . ~ if of the back of the hams, includin three

vi w   1 < . . . g

~', , (Y ' ~ =., '.' 5g digits a half, while the posterior inter-Great occipital § I , ;/ 7 'f .~ . sv osseous is wholly muscular, supplying the nerve ' lf', / t  »., [ ""” ' muscles on the back of the forearm. It Sm=11l<>C¢iDi¢='1l°°-'-" My|, , hy, ,;d gill bg spen tlliat the posterior cord is PGY” ; ' ' /' ~"'~ '* " ~ .. /1 nerve erive a toget er from posterior second-Great 2r1Cl=f VT, V7 f” >l'Q§ , § ary divisions of the plexus, but there N l "ive in, ~ f .(~ ..s;§§ f"" arg tlgrele oqléeli; nerves derived from these gr-veg to eva or ' ug.: ~ r ' y L 7 ~ ~'~~ -Slowking4 —~ ~ ~e fu ' , N w ic s on e mentioned.

anguh scapulae , /H, The posterior thoracic or respiratory Superitial cervical lf / , Hypogmsal gpg!/e of lgell Eomes offh the back of the “ I ff' - /' , sixt an s=vent cervica nerves “we 7 fy/ - I . “ ';' / isixnal laryn- before the anterioriand posterior secondary Spinal accessory, Q/' g ';;§ 1» //4' 'U1>, .7§ /W' eval nerve divisions separate, and runsdown to supply Qi .f 'N .ty rv/ Nerve to the serratus magnus muscle. Nerve to trapeziums, f' f Ili", ' Qt; 11 ', il thYf°'hY°'d The posterior scapular or nerve to the / / A 4 v r, /, .

Ammial branches <0 I. W, w, 7 l Descendens rhomboid muscles runs to those muscles I/VH; -V -, Y, ;f , , li , ,, ,, -; 5 The supra scapular nerve (C, 5, 6) passes Stemal mms '//1 = " 'll "l W" l ' tl r h the si r l t'h L, }-W7 y 71 ljww A MNH » 1; oug 1 p ascapu ar no cf to supp y Posterior scapula: 'f"f? , lf, 'l})M., ”'~ il- tnisdggpraspinatus and in raspinatus honenie, V /%r/ . / tb t 4 " "7!"5M § , § The spinal nerves which are distributed P°5*¢“°"* £22 V/75' / ” 1* £7 lZ'. ' 'lf ~' ' E l t, ' .. to the lower limbs first intercommunicate /' ' " . ~l' ', = Ml l t, "~ ', , ' in the lumbar and sacral plexuses, which, 7/ ff ., . "L l ' 1 'F ll “' with the fperinezg nervesil are sometimes f / ~ X - . 'V /f ~-:;§ , spo ten o toget er as the lumbo sacra

  If 'L T;$ 

Q/ ->Q plexus. The lumbar plexus (see fig. 9) is / A/V, . 1 . QQ formed as a rule of the first four lumbar “I / / ' QV ' nerves, though the greater part of the first I

From A. M. Paterson, in Cunningham's Text-book of Anatomy. FIG. 7.-The Triangles of the Neck (Nerves).

by an overlapping region; and, secondly, that the area supplied by any one spinal nerve is liable to variation in different individuals within moderate limits. This variation may affect the whole plexus, and the term “ prefixed plexus " has been devised by C. S. Sherrington to indicate one in which the spinal nerves entering into its formation are rather higher than usual, while, when the opposite is the case, the plexus is spoken of as “ postfixedl With regard to the muscular supply of a limb the general rule is that each muscle is supplied by fibres derived from more than one spinal nerve; this, of course, is made possible by the redistribution of fibres in the plexuses. Moreover, the muscular supply does not necessarily correspond to that of the overlying skin, because (see MUSCULAR SYSTEM) some of the primitive muscles have been suppressed, others have fused together, while others have shifted their position to a considerable distance. Bearing the foregoing facts in mind, the main distribution of the nerves of the brachial plexus may be surveyed, thou h the exact details must be sought in the human anatomy text-booics. The outer cord of the lexus gives off the external anterior thoracic nerve (C. 5, 6, 7) to the pectoral is major, the musculo-cutaneous nerve (C. 5, 6) to the muscles on the front of the ann, and to the skin of the outer side of the forearm and the number is segmental in its distribution

and resembles one of the thoracic nerves.

It early divides into an ilio-hypngastric

and ilio-inguinal branch, which run

round the abdominal wall in the substance

of the muscles, and of which the former gives off an iliac branch, which is in series with the lateral cutaneous branches of the intercostal nerves and passes over the crest of the ilium to the gluteal region, while the hypo gastric branch runs round to the skin of the pubic region. The ilio-inguinal, on the other hand, gives off no lateral cutaneous or iliac branch, " but is prolonged down the inguinal canal to supply the skin ot the scrotum as well as that of the thigh which touches it. In all probability the hypo gastric branch of the ilio-hypo gastric and the whole of the ilio-inguinal represent the anterior secondary division of the first lumbar nerve, while the posterior secondary division is the iliac branch of the iliohypogastric. The other anterior secondary divisions of the lumbar plexus is the obturator (see fig. 8). The obturator nerve (L. 2, 3, 4) supplies the adductor group of muscles on the inner side of the thig as well as the hip and knee joints; it occasionally has a cutaneous branch on the inner side of the thigh. The posterior secondary branches of the plexus are the genito-crural, the external cutaneous and the anterior crural. The genito-crural nerve (L. I, 2) is partly anterior (ventral) and partly posterior (dorsal). It sends one

anterior branch through the inguinal canal to supply the remaster