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. The muscles 

 operating the lower jaw are also very poorly developed in correlation with the 

 slight mobihty of that member. There are therefore almost no facial muscles. 



A thin flat muscle about 20 nmi. 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 inconspicuous, 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 cm. 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. 



Du-ectly 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 umer 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 thm 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 



