MUSCULATURE. 283 
There remain two additional extensors at the tibial side of the leg. The 
more external arises by muscular fibers from between the heads of tibia and 
fibula, from the interosseous ligament, and mainly from the proximal 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- 
eally 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. Mivart, who regards both these muscles 
in the EKchidna as parts of the tibialis anterior states that the internal 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 hallucis. 
From the foregoing account it is evident that the musculature of the Pro- 
echidna is in the main similar to that of the Echidna. The chief points of differ- 
ence are the following:— the supplementary portion of the lati/ssimus arising 
in the Echidna from the vertebral 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 magnus arises from the four most anterior ribs 
in the Proechidna, whereas in the fchidna 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 to be lacking in the Echidna; the origin of the caput longum 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 vertebral edge of the scapula; 
the flexor profundus digitorwm in the Proechidna sends tendons to digits 2, 3, 
and 4 only, instead of to all five digits of the hand as in the Hechidna; 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 in the hind leg a small muscle probably representing a fleror longus 
hallucis, whose tendon becomes fused with that of the flexor longus digitorum; 
this muscle is not present in the Echidna. 
