REPORT ON THE SEALS. 193 



the migration of a muscle, the anterior part of the semimembranosus in the Phocinas having become 

 an adductor muscle in Arctoccphalus by changing to a more anterior po.sition in the hind limb. 

 The former adducts the thigh and leg and rotates the limb, and the latter adducts the leg and also 

 rotates it. In the Phocinas it is supplied by the obturator nerve. 



The Scmitendinosus, which is named Muse, coccygo-tibialis by Lucae and the semimembranosus 

 by Murie, has two heads of origin. The dorsal head arises from the posterior half of the spine of 

 the last sacral vertebra, from the spine of the 1st caudal vertebra, and is continuous anteriorly with 

 the gluteus maximus. The ventral head arises from the side and ventral surface of the dorsal 

 sacro-iliac ligament, and from the transverse processes and bodies of the 4th and 5th sacral, and the 

 1st and 2nd caudal vertebra. The dorsal head is inserted upon the dorsal surface of the ventral 

 head, half an inch from the caudal vertebrae. The ventral, thus strengthened, passes to the posterior 

 two-thirds of the front of the tibia, into which it is inserted. In Phoca hispida the dorsal part was 

 not seen, and the ventral part was also in a bad state of preservation. It appeared to arise from 

 the 2nd, 3rd, 4th, and 5th caudal vertebrae, and to be inserted into the posterior two-thirds of the 

 front of the tibia above the semimembranosus. In Phoca barbata the dorsal head, or gluteal slip, 

 which is continuous with the hindmost fibres of the gluteus maximus, arises from the 2nd and 3rd 

 caudal vertebras ; the ventral head arises from the 2nd, 3rd, 4th, and 5th caudal vertebras. The 

 insertion is the same as in Phoca hispida. 



In Macrorhinus leoninus there are two heads of origin. The dorsal head arises from the spine 

 of the 2nd caudal vertebra, under cover of the gluteus maximus, and from the dorsal sacro-iliac 

 ligament, as in the others. The fibres are obliquely directed backwards and outwards. It is 

 inserted into the posterior third of the second head near the commencement of the tendon, which is 

 midway between the origin and insertion. The ventral head arises from the sides of the 1st, 2nd. 

 3rd, and 4th caudal vertebrae near the anterior surface of their bodies. Midway between its origin 

 and insertion it forms a very strong broad tendon, which is inserted into the posterior half of the 

 ventral surface of the tibia ; the outer half covers the gracilis. 



In Arctoccphalus gazclla it arises from the transverse processes of the 2nd, 3rd, 4th, 5th, and 6th 

 caudal vertebras, and from the sides of the bodies of these vertebras between the transverse processes 

 and their tubercles. It is inserted into the lower half of the ventral surface of the tibia. In Otaria 

 and Trichcchus it is inserted into the posterior half of the tibia like Arctoccphalus. The action is the 

 same as in the last muscle. Humphry, Lucae, and Murie do not refer to the double mode of origin. 

 In the Phocinas it is supplied by the obturator nerve. 



The Biceps, or ischio-tibialis of Lucae, consists of two distinct muscles, and these are named the 

 Biceps or long head, and the Sacro-peroneus or short head (sacro-fibularis of Lucae). In Phoca vitulina 

 the long head is fan-shaped, and arises from the ischial tuberosity, and from the dorsal and outer 

 surface of it by a pointed fasciculus. It spreads out or radiates towards the fibula. Over the 

 peronei it extends from the head of the fibula almost to the malleoli. Here it is bound to the deep 

 fascia covering the peroneal muscles, and terminates by joining the strong fascia over the outer 

 muscles of the leg, which fascia is bound to the outer and ventral surface of the tibia. The portion 

 at the lower end of the fibula joins the sacro-peroneus and is inserted with it. The short head or 

 sacro-peroneus is riband-like, and arises from the under surface of the dorsal sacro-iliac ligament, 

 from the sides of the 2d and 3rd sacral vertebras. It goes obliquely backward and outward to the 

 lower outer third of the fibula. It is inserted, after joining the former, into the posterior quarter 

 (zool. chall. exp. — paet i.xviii. — 1888.) Yyy 25 



