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



of the dorsal border of the fibula along with the tendon of the long head. In Phoca hispida the 

 long head is the same as in Phoca vitulina, and the short head or sacro-peroneus arises from the 

 4th sacral and 1st caudal vertebrae. In Phoca barbata the biceps (long head) is the same as in 

 Phoca vitulina, and the sacro-peroneus arises from the 2nd and 3rd sacral vertebrae. 



In Macrorhinus leoninus the long head of the biceps arises from the dorsal sacro-iliac ligament 

 opposite the 1st caudal vertebra by a small slip, which blends posteriorly with the ventral part of 

 the semitendinosus, and joins the origin from the tuber ischii 1 inch behind it ; otherwise it is the 

 same as in Phoca vitulina. The sacro-peroneus or short head arises from the ventral and lateral 

 surfaces of the 2nd and 3rd sacral and 1st caudal vertebra;, and from the ventral and lateral 

 surfaces of the dorsal sacro-iliac ligament. It is inserted as in Phoca vitulina. 



In Arctocephcdus gazella the long head of the biceps consists of three parts ; all three arise from 

 the sides of the sacral vertebras. The fibres are transverse and go to the outer anterior surface of 

 the tibia. The anterior part is slightly overlapped by the middle, but the fibres of the middle and 

 posterior parts touch each other. Over the back of the fibula these three form a tendon which 

 turns round the limb to the ventral border. This tendon forms also the deep fascia over the muscles 

 of the leg, and is attached to the tibia, but it does not appear to go to the fibula. The sacro- 

 peroneus or short head arises from the anterior surface of the 4th sacral and 1st caudal vertebrae, 

 and is inserted by a small tendon into the dorsal border of the fibula, over the dorsal malleolus. In 

 all the two heads bend the knee, roll the legs outwards, and adduct them. In Otaria and Trichechus 

 the long head is in two parts. In the Phocinae both the long and the short heads are supplied by 

 the small sciatic. 



The Leg. — The Outer Tibiofibular Eegion in all the specimens has a tibialis anticus, 

 extensor proprius hallucis, and extensor longus digitorum. 



The Tibialis anticus in the Phocinae and Macrorhinus is an elongated triangle with the base 

 at the knee-joint. It is partly under cover of the extensor communis digitorum, and arises from 

 the outer surface of the tibia in its anterior two-thirds, with the exception of a small triangular 

 surface at the upper dorsal part of the head of the shaft, from the ligamentiun patellar, from 

 almost the whole of the anterior two-thirds of the interosseous membrane, and by a small 

 fasciculus from the outer surface of the fibula posterior to the fusion of the bones. Almost at the 

 posterior third of the tibia it forms a strong tendon, which goes through the groove on the outer 

 side of the posterior extremity of the tibia, beneath the annular ligament, and divides into two 

 tendons of equal size. It is inserted into the proximal end of the metatarsal bone of the hallux 

 on its tibial and outer surface, and into the ventral tibial surface of the internal cuneiform. 



In Arctoccphalus gazella it arises from the head and from the outer surface of the tibia in 

 its anterior four-fifths. Near the annular ligament it forms a tendon, which passes beneath it, 

 ventral to the extensor proprius hallucis, and crosses the tarsus, then expands and is inserted into 

 the proximal tibial surface of the 1st metatarsal on its outer side. In Otaria and Triclicchus, besides 

 the insertion, there is also as in Arctocepludus a tendon to the entocuneiform bone. In the Phocinae 

 and Macrorhinus it flexes the ankle, depresses the pes, and turns it outwards. In Arctoccphalus, 

 besides having these actions, it will in walking raise the foot on to the outer edge. Lucae gives only 

 one tendon of insertion, and that to the metatarsal. In the Phocinae it is supplied by the musculo- 

 cutaneous nerve (dorsal division). 



