THE MUSCULO-CUTANEOUS NERVE. 299 



trunk of the median for a variable distance in the upper part of the arm, the musculo- 

 cutaneous or its several branches then being 1 given off from the median tru..k, and pissing 

 outwards to the interval between the biceps and brachialis anticus muscles : this is a common 

 arrangement in lower mammals. In other cases (2 per cent., Testut ; 8 per cent., Villar) only 

 a part of the fibres take this course, so that a communicating branch runs from the median to 

 the musculo-cutaneous (fig. 11)8. 5) ; or the muscular part of the nerve perforates the coraco- 

 brachialis and the cutaneous part is given off from the median (Schwalbe) ; or the median 

 furnishes only the muscular branches (Villar). Much more frequently (36 per cent.. Testut) 

 some of the median fibres are associated with the musculo-cutaneous in its passage through 

 the coraco-brachialis. a communicating branch then passing from the latter nerve to the 

 median. Very rarely the whole outer cord of the plexus pierces the coraco-brachialis, and 

 then divides into musculo-cutaneous and outer head of the median. (Testut, " Recheiches 

 anatomiques sur 1'anastomose du nerf musculo-cutane avec le nerf median," Journ. de 1 Anat., 

 188:5 ; and " Memoire sur la portion brachiale du nerf musculo-cutaue," Internat. Monatschr. 

 f. Anat., 1884; F. Villar, ' Quelques recherches sur les anastomoses des nerfs du membre 

 superieur." Bull. Soc. Anat. de Paiis. 188S.) 



Sometimes the musculo-cutaneous nerve does not perforate the coraco-brrchialis, in which 

 case it may pass eirher behind that muscle, or between the coraco-brachialis and the short 

 head of the biceps. The nerve has also been seen perforating the short head of the biceps, or 

 the brachialis anticus, as well as the coraco-brachialis. 



In rare cases a branch is given to the pronator teres muscle. The terminal porlion of the 

 nerve is not unfrequently continued on the back of the hand to the skin over the first 

 metacarpal bone and the adjoining interosseous space. Hepburn found the musculo-cutaneous 

 supplying the back' of the thumb in a case in which the radial nerve was wanting ; and H. 

 Virchow and Th. Kolliker describe a case in which it gave the dorsal digital nerves to both 

 sides of the ring and the radial side of the little fingers. 



SUMMARY. The musculo-cutaneous nerve supplies the biceps and brachialis 

 anticus muscles, the integument on the outer side of the forearm, the humerus, and 

 the elbow and wrist-joints. Communications are established between it and the 

 radial and the lower external cutaneous branch of the musculo-spiral. 



Ulnar nerve. The ulnar nerve, the largest branch of the inner cord of the 

 brachial plexus, receives its fibres from the last cervical and first dorsal nerves. 

 From its origin, where it is placed between the axillary artery and vein, it descends 

 on the inner side of the main artery of the limb as far as the middle of the arm, and 

 thence with the inferior profunda artery along the back of the internal inter- 

 muscular septum, being often lodged in a grcove in the substance of the inner head 

 of the triceps muscle, to the interval between the olecranon and the inner condyle of 

 the humerus. In the arm it is covered only by the fascia, and it may be felt 

 through the integument a little above the elbow. It next passes between the two 

 heads of the flexor carpi ulnaris muscle, under cover of which it is continued with a 

 straight course as far as the wrist, resting on the flexor profundus digitorum. The 

 nerve meets the ulnar vessels somewhat above the middle of the forearm, and from 

 this point it remains in contact with them on their inner side. Above the wrist it 

 gives off a large dorsal branch to the hand, and the trunk then runs over the front 

 of the annular ligament, being placed between the ulnar artery and the pisiform 

 bone, to terminate as it enters the palm by dividing into superficial and deep parts. 



The ulnar nerve usually gives off no branches in the upper arm. 



A. Branches in the forearm. 



(a) Articular filaments are given to the elbow-joint as the nerve passes 

 behind it. 



(b) Muscular branches (Sc,ld) arise from the nerve near the elbow, and pass to 

 the flexor carpi ulnaris and the inner half of the flexor profundus digitorum muscles. 



(c) Cutaneous branches. These two small nerves arise about the middle of the 

 forearm by a common trunk. One pierces the fascia, and turning downwards, joins 

 a branch of the internal cutaneous nerve : this branch is often absent. The second, 

 a palmar branch, lies on the ulnar artery, which it accompanies to the hand. This 

 little nerve gives filaments around the vessel, and ramifies in the integument of the 



