406 MR. G. E. DOBSON ON THE [Mar. I, 



most superficial of the four in Gymnura, while the least superficial 

 of the three is much smaller than the others. This smaller number 

 of tendons, and evident tendency towards still further reduction, ap- 

 pears to be related to the greater depth of the symphysis pubis, and 

 consequently greater union of the bones of opposite sides, as well as 

 to the lessened proclivity to their separation, owing to the greater 

 transverse diameter of the pelvic opening, which is probably quite 

 sufficient to freely permit of the passage of the foetus during par- 

 turition. 



Qvadratus lumborum is much larger and more fleshy than in 

 Gymnui-a, extending without interruption from the last intercostal 

 space and base of last rib to the crest of the ilium, inserted succes- 

 sively by small tendons into the extremity of each lumbar transverse 

 process. Psoas magnus and psoas parvus are large ; but the latter 

 is inserted into the anterior sacro-iliac ligament and into the margin 

 of the pelvis. 



The jjectoralis major has no separate anterior sternal part, as in 

 Gymnura ; nor has its deep lamina any insertion into the clavicle. 

 The coraco-brachialis, which is altogether wanting in that genus, is 

 well developed here, and consists of two parts: — the superficial, a long 

 slender muscle inserted into the lower third of the humerus ; the 

 deep {coraco-brachialis brevis), short, and inserted below the lesser 

 tuberosity. There is a small teres minor, but, as in Gymnura, no trace 

 of the supinator longus. T\\e palmaris longxis is large, with a distinct 

 tendon, which, passing downwards internal to that of the flexor 

 carpi ulnaris, becomes superficial to it, and glides over the promi- 

 nent pisiform bone (to which the latter is attached) into the hand, 

 becoming there connected with the palmar fascia, and giving origin 

 wholly or in part to the palmaris brevis, from which is derived the 

 flexor perforatus for the poUex and outer finger, the flexor suhlimis 

 digitorum supplying the three middle toes only. Lumbricales, when 

 present, are rudimentary, and connected with the third and fourth 

 digits only. 



In the hind limbs the sartorius, so feebly developed in Gymnura, 

 is represented by two strong muscles ; — one from the fascia covering 

 the iliacus and from the margin of the pelvis in front of the aceta- 

 bulum ; the other, as large, from the margin of the pelvis lower 

 down, midway between the acetabulum and the symphysis pubis. 

 Both are inserted into the tibia, the first above the second, below the 

 attachment ot the internal lateral ligament of the knee-joint. 



These two well-developed muscles are evidently the diflFerentiated 

 representatives of the muscular aponeurosis covering the adductors, 

 and of the small muscle which joins it from the pectineal line in 

 Gymnura. 



The semitendinosus arises simply from the tuber ischii, and is 

 inserted into the tibia behind the tendon of t\\e gracilis; it has no 

 connexion with the biceps flexor cruris. Extensor digitorum longus, 

 as in Gymnura, arises from the external condyle of the femur, and 

 supplies tendons to the four outer toes ; these vary considerably in 

 number, arrangement, and connections with other tendons. The 



