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



The Popliteus in the Phocina? is a triangular muscle with a round tendon. It arises from within 

 the capsule of the knee-joint, from a shallow fossa situated below the termination of the external 

 supracondyloid ridge on the lateral surface of the external condyle. The tendon of origin turns 

 round to the back of the external condyle throughout its posterior surface. It crosses the back of 

 the knee-joint obliquely from without inwards, and is inserted into the upper third of the ventral 

 border of the tibia, into the inner part of the ventral tuberosity, into the whole extent of the dorsal 

 side of the internal lateral ligament, and into the inner surface of the tibia anterior to the feebly 

 marked oblique line posterior to this ligament. 



In Macrorhinus leoninus the tendon arises below a slight depression on the lateral side of the 

 external condyle ; otherwise as in Phoca vitidina. It is inserted into the well-marked triangular 

 surface anterior to the oblique line of the tibia ; otherwise as in Phoca. 



In Arctocephalus gazella it is larger than in the Phocinse. It arises from the external surface 

 of the external condyle by a strong round tendon, which forms part of the capsule of the knee- 

 joint, and by the same origin as the plantaris from the femur. The latter origin at once becomes 

 muscular and covers the round tendon. The two heads blend over the back of the knee-joint, 

 and cross between the outer condyle of the femur and the head of the fibula. It is inserted, 

 into the anterior two-thirds of the inner surface of the tibia dorsal to the internal lateral ligament 

 and ventral to the popliteal line. The internal lateral ligament only extends backwards to the 

 middle of the shaft. It bends the knee and rolls the leg inwards. 



There is in all the specimens a groove upon the external condyle of the femur for the tendon of 

 the popliteus. The oblique line runs from the junction of the external and internal tuberosities on 

 the inner surface of the tibia, backwards and downwards to join the ventral border of the tibia. 

 This is very different from human anatomy, where it runs from the fibular facet of the tibia to 

 the internal border. The oblique line in Macrorhinus is more like what is seen in man. In the 

 Phocinae the muscle is supplied by the great sciatic nerve. 



The Flexor longus hallucis is the flexor digitorum of Humphry; in Phoca vitidina it is an elon- 

 gated fusiform mass of fibre, and is the largest of the deep flexors of the back of the leg. It arises 

 from the inner surface of the fibula, going backwards to its posterior extremity, from the inner 

 surface of the head, and from the interosseous membrane. It just overhangs the ventral border of 

 the fibula, and does not encroach far upon the interosseous space. The flexor longus digitorum 

 touches its border and the tibialis posticus lies to its ventral side. Anterior to the inner surface of 

 the ankle-joint it forms a tendon which is broad, flat, and strong ; this runs in a groove on the 

 backward projection of the astragalus through a fascial tunnel formed by the annular ligament. In 

 Phoca hispida and in Phoca barbata the origins and insertions are similar to those in Phoca vitidina., 

 but the development is much more perfect in the two former than in the latter, the bellies being 

 much larger and more fusiform. It can with safety be said that the bellies were enormous for the 

 size of these two animals. 



In Macrm-hinus it is like that in Phoca vitidina, but in addition there was a dense fascia over 

 its anterior surface. The belly was the same as in Phoca vitidina, but only of moderate size. 



In Arctocephalus gazella it arises from the inner surface of the head of the fibula, from the inner 

 surface of the anterior fourth of the shaft, and by an aponeurosis from the tibia, which gradually 

 passes from its dorsal border to the short inner border on the posterior two-thirds of the shaft. 

 Near the ankle it forms a tendon, which runs beneath the annular ligament in the groove on the 



