DISSECTION OP THE ANTERIOH LIMB. 21 



insertion from the biceps, and another from the scapulo-ulnaris ; below 

 it is continued over the carpus to form sheaths for the tendons ; while 

 by its deep face it furnishes septa to pass between the muscles of the 

 fore-arm. 



Directions. — The dissection of the back of the fore-arm is now to be 

 undertaken. The before -mentioned fascia is to be incised along the 

 lines of separation of the muscles, and these are to be cleaned and 

 isolated. The remaining portion of the posterior superficial pectoral 

 muscle, which covers the posterior radial vessels and the median nerve 

 at the inner side of the elbow, is to be removed ; and care is to be 

 taken of the iilnar vessels and nerve, which are placed beneath the 

 deep fascia, on the middle line at the back of the limb. 



The Ulnar Abtbby (Plates 6 and 7) is a collateral branch of the brachial, 

 from which it comes oiF at the lower border of the caput parvum. It 

 descends parallel to the lower border of that muscle, to the space between 

 the olecranon and the inner condyle, where it is covered by the scapulo- 

 ulnaris. It here places itself in company with the ulnar nerve ; and, 

 crossing beneath the ulnar origin of the middle flexor of the metacarpus, 

 it descends to the carpus by following the tendon of the ulnar portion of 

 the deep flexor (ulnaris accessorius), being placed between the external 

 and oblique flexors of the metacarpus. At the upper limit of the carpus 

 it concurs in the formation of the supracarpal arch, by joining a branch 

 detached from the large metacarpal artery. In this course it gives off 

 — (1) the nutrient artery to the humerus (sometimes); (2) articular 

 branches to the elbow-joint ; (3) muscular branches in the neighbour- 

 hood of the joint, to the scapulo-ulnaris, caput parvum, and posterior 

 superficial pectoral ; (4) cutaneous branches to the skin on the inner 

 side of the fore-arm. 



The Ulnar Vein accompanies the artery and nerve, and at the elbow 

 concurs in the formation of the brachial vein. 



The Ulnar Nerve (Plates 6 and 8) has already been partly described in 

 the dissection of the arm. At the lower part of that region it crosses 

 the ulnar artery, with which it places itself in company between the ole- 

 cranon and the inner condyle. It here gives off branches to the following 

 muscles : — (1) the anterior head of the middle flexor of the metacarpus ; 

 (2) the ulnar head of the same muscle ; (3) the superficial flexor of the 

 digit (perforatus) ; (4) the ulnar origin of the deep flexor (ulnaris 

 accessorius). In the fore-arm it descends in close company with the 

 vessels of the same name, and at the carpus it gives off' the cutaneous 

 branch already described (page 20). At the upper border of the pisiform 

 bone, and beneath the tendon of the middle flexor,* it joins a branch 

 from the median to form the external plantar nerve. 



* In Plates 6 and 9 the termination of the nerve has been pulled slightly forwards to show its 

 junction with the branch from the median. 



