MUSCULATURE. 283 



There remain two additional extensors at the tibial side of the leg. The 

 more external arises l)y muscular fibers from between the heads of tibia and 

 fibula, from the interosseous ligament, and mainlj^ from the proxmial two 

 thirds of the shaft of the tibia. At the tarsus it becomes a flat tendon passing 

 to the external side of the first digit. Closely applied to this muscle and practi- 

 cally united with it at the origin along the anterior side of the tibia, is a second 

 'and broader muscle likewise passing to a tendon that inserts beside the first 

 on the dorsal surface of the hallux. jMivart, who regards both these muscles 

 in the Echidna as parts of the tibialis anterior states that the intern;^,! tendon 

 passes beneath the external at the insertion, but this is not true in the Pro- 

 echidna. Probably Westling is correct in considering the more internal of 

 these two muscles the tibialis anterior (Plate 1, fig. 1, ta) and the more external 

 the extensor longus halliicis. 



From the foregoing account it is evident that the musculature of the Pro- 

 echidna is in the main smiilar to that of the Echidna. The chief points of differ- 

 ence are the following: — the supplementary portion of the latissimus arising 

 in the Echidna from the \'ertebral angle of the scapula, originates instead from 

 the ridge just dorsal to the glenoid cavity, and here sends out a second branch 

 to the olecranon; the serratus viagnus arises fi'om the four most anterior ribs 

 in the Proechidna, whereas in the Echidna the five anterior ribs are involved; 

 the rectus capitis lateralis is from the axis in the Proechidna instead of from 

 the atlas; a single median muscle, apparently a sternohyoideus is present, but 

 seems t'O be lacking in the Echidna; the origm of the caput longwm of the triceps 

 is short, from the ridge on the scapula just dorsal to the glenoid cavity, whereas 

 in the Echidna the origin extends nearly to the A'ertebral edge of the scapula; 

 the flexor profundus digitorum in the Proechidna sends tendons to digits 2, 3, 

 and 4 only, instead of to all five digits of the hand as in the Echidna; this differ- 

 ence, correlated with the reduction of the clawed digits to three in the former, 

 seems of considerable importance, since the functional loss of digits 1 and 5 is 

 correlated with the disappearance of their respective flexors; in the manus of 

 the Proechidna a muscle apparently representing the abductor digiti quinti 

 is present, but seems to be absent in the Echidna; an adductor longus of the hind 

 leg seems to be wanting in the latter but is present in the Proechidna; there is 

 also present m the hind leg a small muscle probably representing a flexor longus 

 hallucis, whose tendon becomes fused with that of the flexor longus digitorum; 

 this muscle is not present in the Echidna. 



