520 



ZOOLOGY 



SECT. 



which supports the horny teeth {dent) of the upper jaw. The 

 nasal and premaxillar}^ region is expanded into a rostrum, which 

 is mnch broader than in Echidna. The premaxilke (jir. ma.r.) 

 diverge from one another anteriorly, and then curve inwards again, 

 partly enclosing a large space in which the nostrils are situated, 

 and which is covered over in the recent state by the tough but 

 sensitive, hairless integument investing the cartilage of the 

 rostrum, the latter being continuous with the nasal septum. In 

 this space between the premaxillaj is situated a dumb-bell shaped 

 bone (x) which appears to be of the nature of an anterior vomer. 

 The pterygoid {'pter.) is much smaller than in. Echidna, and 

 does not extend so far back as the tympanic cavity. The 

 mandible has its rami stouter than in Echidna; they meet 

 for a short distance anteriorly, and then again diverge 

 slightly. The condyle is much larger than in Echidna, and is 

 elongated transversely. In front of it is a broad process bearing 

 the horny tooth. 



It is in the shoulder girdle that we find perhaps the most 

 striking peculiarities of the skeleton of the Prototheria. There is 

 a T-shaped episternum {cpist.), as already stated, similar to that 

 of Keptiles, the median limb articulating behind with the pre- 

 sternum and the cross-piece closely applied 

 to the clavicles. There are two short and 

 broad coracoids {cor.) articulating internally 

 and behind with the presternum, and, 

 externally, uniting with the scapula to 

 form the glenoid cavity. In front of the 

 coracoid is a flat plate, the epicoracoid 

 {ep.cor.). The scapula (Fig. 1129) is very 

 unlike that of other Mammals. There is a 

 well-developed acromion process {acr.) with 

 wdiich the clavicle articulates; this ter- 

 minates the anterior border, so that the 

 latter would appear to correspond to the 

 spine of the scapula of other Mammals : 

 this is confirmed by the arrangement of 

 the scapular muscles. The anterior part of 

 the inner surface is in reality the prc- 

 spinous fossa; the anterior portion of the outer surface the post- 

 spinous fossa ; and the part behind this, separated from it by 

 a slight ridge, together with the posterior portion of the inner 

 surface, is the subscapular fossa. 



The humerus is of remarkable shape, wdth greatly expanded 

 extremities — esi^ecially in Echidna — and prominent tuberosities 

 and condyles. In the carpus the scaphoid and lunar are united ; 

 there is no separate centrale. There is a radial sesamoid, and two 

 very large palmar sesamoids, which are sometimes united. 



acr' 



giert 



Flo. 1120.— Outer surface of 

 left scapula of Ornitho- 

 rbyncbus. ocr. process 

 corresponding to acromion ; 

 (ilcii. glenoid ai-ticular sur- 

 face ; .«p. anterior border, 

 corresponding to the spine ; 

 .1', slight ridge which boinids 

 the surface of origin of the 

 sub-scapularis muscle an- 

 teriorly. 



