THE BRACHIAL PLEXUS. 845 



Mr. Hilton takes the circumflex nerve as an illustration of a law which he lays down, that 

 " the same trunks of nerves whose branches supply the groups of muscles moving a joint furnish 

 also a distribution of nerves to the skin over the insertions of the same muscles, and the interior 

 of the joint receives its nerves from the same source." In this way he explains the fact that an 

 inflamed joint becomes rigid, because the same nerves which supply the interior of the joint 

 supply the mus vies also which move that joint. 



The median ///? is liable to injury in wounds of the forearm. When paralyzed, there is 

 f flexion of the second phalanges of all the fingers and of the terminal phalanges of the 

 index and middle fingers. Flexion of the terminal phalanges of the ring and middle fingers is 

 effected by that portion of the Flexor profundus digitorum which is supplied by the ulnar nerve. 

 There is power to flex the proximal phalanges through the Interossei. The thumb cannot be 

 flexed or opposed, and is maintained in a position of extension and adduction. All power of 

 pronation is lust. The wrist can be flexed, if the hand is first adducted. by the action of the 

 Flexor carpi ulnaris. There is loss or impairment of sensation on the palmar surface of the 

 thumb, index, middle, and outer half of the ring fingers, and on the dorsal surface of the same 

 fingers over the last two phalanges : except in the thumb, where the loss of sensation would be 

 limited to the back of the last phalanx. In order to expose the median nerve for the purpose 

 of stretching an incision should be made along the ulnar side of the tendon of the Palmaris 

 longus. which serves as a guide to the nerve. 



The ii.finn' nerve is also liable to be injured in wounds of the forearm. When paralyzed, 

 there is loss of power of flexion in the ring and little fingers : there is impaired power of ulnar 

 flexion and adduction : there is inability to spread out the fingers from paralysis of the Inter- 

 and there is inability to adduct the thumb. Sensation is lost or impaired in the skin sup- 

 plied by the nerve. In order to expose the nerve in the lower part of the forearm, an incision 

 should be made along the outer border of the tendon of the Flexor carpi ulnaris. and the nerve 

 will be found lying on the ulnar side of the ulnar artery. 



The musculo-spira! nerve is probably more frequently injured than any other nerve of the 

 upper extremity. In consequence of its close relationship to the humerus as it lies in the mus- 

 culo-spiral groove, it is frequently torn or injured in fractures of this bone, or subsequently 

 involved in the callus that may be thrown out around a fracture, and thus pressed upon and its 

 functions interfered with. It is also liable to be contused against the bone by kicks or blows or 

 to be divided by wounds of the arm. When paralyzed, the hand is flexed at the wrist and lies 

 flaccid. This is known as " drop-wrist" The fingers are also flexed, and on an attempt being 

 made to extend them the last two phalanges only wilTbe extended through the action of the Inter- 

 the first phalanges remaining flexed. There is no power of extending the wrist. Supina^ 

 tion is completely lost when the forearm is extended on the arm. but it is possible to a certain 

 extent if the forearm is flexed so as to allow of the action of the Biceps. The power of exten- 

 sion of the forearm is lost on account of paralysis of the Triceps. The best position in which 

 to expose the^ nerve for the purpose of stretching is to make an incision along the inner 

 border of the Supinator longiis. just above the level of the elbow-joint. The skin and super- 

 ficial structures are to be divided and the deep fascia exposed. The white line in this struc- 

 ture indicating the border of the muscle is to be defined, and the deep fascia divided in this 

 line. By now raising the Supinator longus the nerve will be found lying beneath it, on the 

 Brachialis antieus. 



THE DOESAL NERVES (Fig. 502). 



The Dorsal Nerves are twelve in number on each side. The first appears 

 between the first and second dorsal vertebrae, and the last between the last dorsal 

 and first lumbar. 



The roots of tln> dorsal nerves are of small size, and vary but slightly from the 

 second to the last. Both roots are very slender, the posterior roots only slightly 

 exceeding the anterior in thickness. They gradually increase in length from 

 above downward, and pass down in contact with the spinal cord for a distance 

 equal to the height of, at least, two vertebrae, in the lower part of the dorsal region, 

 before they emerge from the spinal canal. They then join in the intervertebral 

 foramen, and at their exit divide into two primary divisions, a posterior (dorsal) 

 and an anterior (intercostal). 



The first and last dorsal nerves are peculiar in some respects. 



Posterior Divisions of the Dorsal Nerves. 



The posterior divisions of the dorsal nerves, which are smaller than the ante- 

 rior, pass backward between the transverse processes, and divide into internal and 

 external branches. 



The internal branches of the six upper nerves pass inward between the Semi- 

 spinalis dorsi and Multifidus spinae muscles, which they supply, and then, piercing 



