184 THE VOYAGE OF H.M.S. CHALLENGER. 



In Macrorhinus, and in all the femora of the Phocinae, there is an oblique ridge running from 

 the top of the great trochantei on the front surface to the external condyle, which curves out- 

 wards in Macrorhinus to below the middle of the head of the femur before going to the external 

 condyle (PI. IV. fig. 4). In Arctocephalus the ridge is not well marked, but above the line on the 

 femur for the capsular ligament of the knee in the middle of the shaft, a ridge from the top of the 

 great trochanter runs down the upper third of the shaft in a line with this point (PI. VII., fig. 7). 

 This ridge marks off the vastus externus, even although the fibres of the crureus pass in below it 

 for a distance. In the Phocinae the vastus externus is supplied by the anterior crural nerve. 



The Crureus. — In all the specimens there is a layer of muscular fibres without a natural division 

 covering the front of the femur, which may be the combined vastus internus and crureus, but 

 certainly is not the vastus internus only. For in Arctocephalus there is a large internal surface on 

 the femur, and if it were covered by muscular fibres going to the patella, that would afford 

 sufficient proof that it was the vastus internus. The fibres on the front surface, however, run from 

 the ventral side of the internal condyle to the corresponding surface of the neck, and do not cover 

 any part of the extensive internal surface of the shaft, therefore the group of fibres is more entitled 

 to the name of crureus in Arctocephalus and still more so in the Phocinas where there is no internal 

 surface. 



In the Phocinaj it arises from the anterior surface of the femur, from the intertrochanteric 

 line. It extends down the shaft to the part which is covered by the capsular ligament of the knee- 

 joint, and is inserted into the upper edge of the patella beneath the rectus, into the outer upper 

 half of it (the muscular fibres descend no further), into the inner side of the ligamenturn patellae, 

 into the head of the tibia on the ventral side, and into the capsule of the knee-joint. 



In Macrorhinus Iconinus it is similar, with the exception of its insertion into the inner side of 

 the patella. The muscular fibres stop at the lower inner edge of it, and are inserted into the inner 

 side of the head of the tibia by a tendon. 



In Arctocephalus gazella it arises from the front surface of the femur, with the exception of the 

 surface occupied by the vastus externus, and is inserted into the capsule of the knee-joint, and into 

 the upper edge of the patella. In Otaria and Tricheehus it is combined inseparably with the 

 vastus externus. 



Lucae describes the vastus externus and crureus as a combined muscle, thus recognising the 

 presence of both ; and I found them in all the dissections, including that of Arctocephalus. Although 

 the vastus externus is not perfectly separate, the direction of the fibres is an aid to its recognition 

 as a distinct muscle. In Macrorhinus the separation is further assisted by a tendinous surface upon 

 the posterior portion of the externus, and here the distinction of it from the crureus was easier. In 

 Phoca it was not so distinct, and less so in Arctocephalus; but in all it merited a special 

 description. Dr. Murie describes in Otaria and Tricheehus the internus and externus, and is 

 doubtful about the crureus. As already explained, the vastus internus would go over the internal 

 surface if it were present as it is in Arctocephalus; when this surface gives no origin to the 

 internus, then the crureus must be crowded out by the two lateral muscles encroaching upon its 

 surface of origin, for in the Phocinae, where there is no internal surface, there is the same collection 

 of fibres with the same insertion as in Arctocephalus, so I conclude that in Arctoccplmlus there is a 

 crureus and vastus externus, whereas Otaria and Tricheehus have a vastus externus and internus. 

 The extensor of the leg, as the name implies, will extend it and flex the thigh upon the pelvis. The 



