488 



ZOOLOGY SECT. 



united with the periotic. The mandible consists of very narrow, 

 styliform rami, which are not firmly united at the symphysis. 

 The condyle (cond.) is narrow, rather more elongated antero- 

 posteriorly than transversely. There are very slight rudiments 

 of the angle and of the coronoid process (cor.). 



In the Platypus (Fig. 1058) the zygoma is stouter than in 

 Echidna, and there is a rudimentary post-orbital process. The 

 maxillary root of the zygoma develops a process which supports the 

 horny teeth (dent.) of the upper jaw. The nasal and pre-maxillary 

 region is expanded into a rostrum which is much broader than 

 in Echidna. The premaxillse (pr. max.) 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 

 covering over the cartilage of the rostrum, the latter being con- 

 tinuous with the nasal septum. In this space between the pre- 

 maxillae 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 ;han 

 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 epi-sternum (cpist.), as already stated, similar to that ot 

 Reptiles, 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 pre-sternum, and, exter- 

 nally, uniting with the scapula to form the 

 glenoid cavity. In front of the coracoid is 

 a fiat plate, the epicoracoid (ep. cor.). The 

 scapula (Fig. 1060) is very unlike that of 

 other Mammals. There is a well-developed 

 acromion process (acr.) with which the 



ri jy srapTiif o7 ornit e ho f clavicle articulates ; this terminates the 

 rhyncnus. acr. process anterior border, so that the latter would 

 yS'SSf&Stt appear to correspond to the spine of the 

 tSJtS&?3Si scapula of other Mammals. This is con- 

 a?, slight ridge wMeh bounds firmed bv the arrangement of the scapular 



the surface of origin of the / 3 . ,. ,1 



sub-scapuiaris anteriorly. muscles. The anterior part or 



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, 



