MUSCLES OF THE HIND LIMB. 29 



posterior side. Tiiis muscle in Centetes is similar but with a rather more 

 extensive distal insertion, wliile in Gymnura the insertion is nearer the proxi- 

 mal end of the femur. 



The adductor magnus (Plate 4, fig. 2, m) is small. It is a thin narrow strip 

 arising from the tuberosity of the ischium untler the biceps, and passes to an 

 insertion under cover of that of the adductor longus on the internal condyle of 

 the femur. This muscle shows a less developed condition as compared with 

 that of Gymnura and Centetes. The peculiar insertion into the inner head of 

 the gastrocnemius described by Dobson in Potamogale, he believes is a special 

 mocUfication correlated with the animal's habit of drawing the hind leg up 

 against the tail when swimming. 



The origin of adductor quartus (Plate 4, fig. 2, k) is under cover of that of 

 adductor brevis from the ventral portion of the pul)is antl ischium, but its pos- 

 terior extent is less at the ventral margin. It increases sliglitly in breadth as 

 it passes over the lesser trochanter to insert on the proximal third of the femur 

 along the ento-posterior side of the great trochantal ritlge nearly to the proximal 

 insertion of the adductor brevis. In Centetes and Potamogale according to 

 Dobson, this muscle presents the same relations, but it appears to be absent in 

 Gymnura. 



The gastrocnemius (Plate 6, fig. 1, e; fig. 4) is a large muscle arising by two 

 heads as usual. The first is from the posterior side of the external condyle of 

 the humems, by a stout tendon in wliich there is a small sesamoid bone; the 

 second is from the internal condyle just proximal to the insertion of a portion 

 of the semimembranosus to which it is joined by a few fibers. The great nerve 

 tnmk of the leg passes between these two heads. The insertion is as usual by 

 the tendon of Achilles into the calcaneum at its posterior end. 



The salens (Plate 6, fig. 4, o) shows an interesting relaticjn, and one appar- 

 ently not observed by Dobson in Solcnodnn cubanus. It arises by tendinous 

 fibers from the ecto-posterior edge of the head of the fibula, and becomes fused 

 with the ectal portion of tlie gastrocnemius above its passage into the tendon of 

 Achilles. A similar condition is found in Gymnura and Potamogale, but appar- 

 ently not in Centetes. 



The jdantaris resembles that of Centetes in being inseparable from the gas- 

 trocnemius at its origin. Its tendon is apparent, however, on the ento-lateral 

 side of the gastrocnemius. In Gymnura and Potamogale the origin is described 

 as distinct from that of the latter. 



The popliteus arises as usual from the thick tendon investing the ectal side 



