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



surface of the tibia, extending to the external border. It draws the leg inwards, and in Arctoccphcdus 

 will turn the leg inwards when progressing on land. In Otaria a few fibres overlap the external 

 oblique, but in Trichcchus it has no fibres covering this muscle, and so is similar to Arctocephalus. 

 In the Phocinae it is supplied by the obturator nerve. 



The Semimembranosus is named Muse, pubo-tibialis by Lucae ; in PJioca vitulina it lies above the 

 gracilis and is partially hidden by it. It is in two parts, the anterior and posterior. The anterior 

 arises from the outer surface of the innominate bone posterior to the foramen, in front of the origin 

 of the posterior part, and above the origin of the gracilis. It is inserted into the posterior two- 

 thirds of the front of the tibia, its tendon combining with the gracilis. The posterior part arises 

 from the outer edge of the innominate, between the tuber ischii, from which it also has fibres of 

 origin, and the origin of the anterior part from the pubic bone. It is inserted into the tibia, 

 anterior to the seniiinembranosus (anterior part), and extends forwards to one-fifth from the upper 

 extremity of the tibia. In Phoca hispida the anterior part arises from the outer surface of the 

 innominate bone, from the body of the pubis upwards to where the pubis and ischium fuse, and 

 from the edge of the bone between the origin of the gracilis to the semimembranosus (posterior 

 part). It is inserted into the posterior half of the ventral surface of the tibia, in conjunction with 

 the semitendinosus and hinder three-fourths of the gracilis. The posterior part is placed above 

 the gracilis. It arises from the outer dorsal half of the pubic bone, between the tuber ischii and 

 the origin of the semimembranosus anterior part, slightly from the base of the tuber posteriorly, and 

 from the edge of the bone between these two points. It goes outwards and forwards, and is 

 inserted into the ventral surface of the tibia in its upper half, the fibres almost reaching the head 

 of the shaft. In Phoca barbata both parts are similar to the last, except that the origin does not 

 go up to the tuber ischii, and the insertion is smaller, not reaching so far forwards on the tibia, 

 but falling short of the head by a quarter of the length of this bone. 



In Macrorhinus leoninus it is almost the same as is the posterior part in Phocinse. It arises 

 from the outer surface of the innominate bone, posterior to the origin of the adductor longus and 

 that part of the obturator externus which represents the quadratus femoris, extending backwards a 

 little more than halfway between the symphysis and the ischial tuber. It is inserted into the 

 anterior half of the ventral surface of the tibia, reaching almost to the head of the bone. 



In Arctocephalus yazella it is closely allied to the posterior part in Phoca vitidina, Phoca hispida, 

 and Phoca barbata. It arises from the posterior third of the outer edge of the pubic bar, which is 

 behind the rudimentary tuber ischii, from the third of the posterior border of the innominate bone, 

 which is the continuation of the sitting bone downwards, and slightly from the surface of the 

 innominate adjoining the marginal origin. It is inserted into the front of the tibia in front of 

 the semitendinosus, the fibres terminating a quarter of the length of the tibia from the head of the 

 shaft, i.e., it is inserted into the second fourth of the tibia from the head. Lucae describes it as one 

 part in Phoca. In Otaria, what Murie names semitendinosus I call semimembranosus ; this also 

 applies to Trichcchus. 



In all the specimens the posterior part is present ; in Macrorhinus and Arctoccphcdus the 

 anterior part is wanting. The insertion of the posterior part in all is nearer the tibial head, the 

 insertion in Macrorhinus almost touching it. The portion of bone giving origin to the anterior part 

 in the Phocinaa is utilised in Arctoccphcdus for the adductor magnus, and in the latter it has 

 wandered up the limb and divides its attachment between the femur and tibia. This is a case of 



