REPORT ON THE SEALS. 171 



supracondyloid ridge, and in Arctoccphalus and Otaria from it and the external condyle, it is 

 difficult to comprehend whether it is a single muscle with a divided tendon, or the longus and 

 brevis united. The action of the extensor carpi radialis longus and brevis in human anatomy is 

 to extend the wrist, but after this is done the longus can flex the arm. In the Seals both actions 

 can be performed, and thus the function of this muscle is that of the longus and brevis. 



The lower end of the radius in the Phocinse and Arctocephalus has a characteristic difference. 

 The scapholunar bone in the former has a very large radial tubercle, in Arctoccphalus a small one, 

 and in the latter the lower end of the radius articulates almost entirely with the scapholunar. In 

 the Phocinre the large tubercle seems to be formed at the expense of the scapholunar, for this bone 

 only articulates with half of the lower end of the radius : hence the outer lower half of the radius 

 is non-articular, the inner being the articular surface. It is supplied by the musculo-spiral 

 nerve. 



The Extensor communis digitorum is a double muscle consisting of two separate origins ; these 

 are named primus and secundus. a. The extensor communis digitorum primus is named by Vrolik 

 M. digitorum extensores ; by Humphry, extensor communis digitorum ; by Lucae, mus. extensor 

 cpiatuor digit. ; and by Murie, extensor. It cerises from the supracondyloid ridge, below the extensor 

 carpi radialis. At the middle of the arm it forms a flat tendon, which passes through the third 

 division of the annular ligament. Above the bases of the metacarpal bones the tendon expands 

 and breaks into four tendinous slips, which pass down between the metacarpal bones to the radial 

 sides of the four fingers. At the middle of the 1st phalanges the tendons begin to expand 

 towards the ulnar sides of these bones, and at the heads of the 2nd phalanges the tendons cover 

 the entire dorsum. They proceed to the bases of the 3rd phalanges, where they are inserted. 

 The tendons adhere closely to the posterior ligaments of the joints of the digits, b. The extensor 

 communis digitorum secundus. Vrolik appears to call it the extensores digitorum communes breves, 

 Humphry the extensor secundus digitorum, Lucae the mus. abductor quatuor digitorum. It arises 

 from the supracondyloid ridge below the primus, and from the external condyle. It slightly over- 

 laps the primus ; and a little below the middle of the forearm divides into four tendons, which 

 pass through the fourth division of the annular ligament posterior to the primus. Two of the 

 tendons pass outwards beneath the tendons of the primus, and run down the ulnar sides of the 

 2nd and 3rd metacarpal bones. The 3rd runs down the ulnar side of the 4th metacarpal 

 bone, and the 4th divides into two, one going to each side of the 5th metacarpal. The tendons 

 of the 2nd, 3rd, and 4th metacarpals are inserted into the heads of the ulnar sides of these bones, 

 and into the dorsal surfaces of the proximal ends of the 1st phalanges, and also into their ulnar 

 sides. The tendon of the 5th metacarpal splits into two as before stated ; the anterior one is 

 inserted into the radial side of the head of the 5th metacarpal, and into the dorsum and ulnar 

 side of the proximal end of the 1st phalanx ; the posterior into the dorsum and head of the 5th 

 metacarpal. 



In Arctoccphalus it arises from the external supracondyloid ridge, and from the extensive 

 lateral ligament beneath the muscle. It passes to the interosseous space and divides into two 

 slips, which cross the extensor pollicis proprius. From these two slips are formed the outer slip 

 or extensor communis digitorum, and the inner or extensor minimi digiti. The extensor communis 

 digitorum divides into four tendons. The 1st descends along the ulnar side of the 2nd metacarpal 

 bone ; the 2nd along the dorsum of the 3rd ; the 3rd descends upon the radial side of the 4th ; 



