MUSCULATURE. 263 
peroneal aspect of the tibia. A similar condition is described in the case of the 
Echidna by Fewkes. 
MUSCLES OF HEAD AND NECK.— The muscles of the head appear to resemble 
those of the Echidna in all essential respects. The long snout is covered by 
thin hardened cuticle quite without any evident musculature. Themuscles 
operating the lower Jaw are also very poorly developed in correlation with the 
slight mobility of that member. There are therefore almost no facial muscles. 
A thin flat muscle about 20 mm. wide arises by thin connective tissue from 
the parietal region under the anterior edge of the panniculus and passes to the 
posterior edge of the opening of the external ear. Its homology is not altogether 
certain. 
The digastric muscle is a short narrow strand from the skull just anterior 
to the ear, to the posterior corner of the angle of the jaw. 
The masseter is also mconspicuous, arising from the posterior half of the 
ventral margin of the zygomatic arch. It inserts in a shallow depression on the 
external side of the mandible from the angle of the jaw to a small prominence 
about 1 em. in advance that may be considered a coronoid process. In the 
Echidna this muscle is described as considerably larger, with an origin about an 
inch in length, from a point “about half an inch in advance of the anterior edge 
of the orbital foramen.” 
The temporalis fills the posterior half of the orbit, where its origin is 
only about 1 cm. in length. It narrows to its insertion on the coronoid 
process. 
Directly under and posterior to this is the pterygoideus internus, which 
arises from the skull by muscular fibers from the insertion of the temporalis 
to the glenoid cavity of the jaw. It inserts on the inner side of the jaw from 
the condyle to the coronoid process, and is about as large as the temporalis. 
The pterygoideus externus is smaller and arises posterior to the pterygoideus 
internus and inserts on the inner side of the condyle of the jaw. The condition 
is apparently the same as in the Echidna, as minutely described by Lubosch 
(1906, p. 558). The homology of these muscles with the pterygoidei of other 
mammals is uncertain. 
The trapezius muscles, as in the Echidna, consist of an anterior and a pos- 
terior. The former arises by a thin tendinous sheet from the entire midline 
of the neck and mainly from the side of the occiput, dorsal to the ear. It inserts 
along the dorsal half of the clavicle and the anterior edge of the scapula, where 
its fibers join those from the second or posterior portion at the anterodorsal 
