xm PHYLUM CHORDATA 505 



partly enclosing a large space s 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 premaxillse 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 as 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 Pro t other ia. There is a 

 T-shaped episternum (epist.), as already stated, similar to that 

 of Keptiles, the median limb articulating 

 behind with the presternum 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. 

 1141) is very unlike that of other Mammals. 

 There is a well-developed acromion process 

 (acr.) with which the clavicle articulates ; 

 this terminates the anterior border, so that 

 the latter would appear to correspond to *, slight ridge which bounds 



, ,, ,, r , the surface of origin of the 



the spine ot the scapula of other Mammals : sub-scapuiaris muscle an- 

 this is confirmed by the arrangement of the 



scapular muscles. The anterior part of the inner surface is in 

 reality the pre-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 sub-scapular fossa. 



The humerus is of remarkable shape, with greatly expanded 

 extremities especially in Echidna and prominent tuberosities 

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

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

 very large palmar sesamoids, which are sometimes united. 



In the pelvis there is a very long symphysis in which pubes 

 and ischia take an almost equal share. The acetabulum is per- 

 forated in Echidna. With the anterior border of the pubes are 

 articulated a pair of large epipubic or " marsupial " bones (Fig. 1139, 

 ep. pb.). The femur has expanded extremities with prominent 

 external and internal trochanters. There is a large ossified patella 



