RHIZOMYS. 



317 



The scapula of B.prtiinosus and of B. badius are essentially like that of Slphieus, 

 and when they are described as only more elongated and broader across the neck of 

 the bone than in ordinary rats, some idea of their form will have been conveyed. The 

 acromio-scapular notch is not so deep as in the rat, and the acromion is more 

 forwardly projected than in that animal and has great expansion. 



The OS innominatum conforms to the Arvicoline type, but the thyroid foramen is 

 much longer than in Siphneus, and the pubic and ischial bones are weaker and less 

 expanded, the former being reduced to a narrow rod. There are also certain 

 remarkable differences between the pelves of these two forms. In B. baclius the 

 thyroid foramen is quite as small as in Siphneus, and the symphysis pubis, 

 which is rather deep in B. pruinostis, is the very opposite in the former species. 

 In both, anchylosis has taken place through the intervention of a triangular 

 epiphysis, but, even with the aid of this, the symphysis is not so deep as in Mus 

 decumanus. 



The sexual characters of the pelves of these species are very well defined, the 

 transverse breadth of the symphysis being much greater in the female than in the 

 male. 



The skull has been described by Temminck, and its general characters indicated 

 by A. M. -Edwards, so that nothing remains to be said under this head, except 

 that the periotic bullge are weU developed on the posterior aspect of the skull, behind 

 the auditory osseous tube. Three prominent transverse grooves occur on the anterior 

 portion of the palate, immediately before the molars, and are succeeded by four much 

 more obscure furrows between the teeth. 



In a young example of B. pruinosus, Blyth, the incisor teeth are well exposed, 

 but none of the upper or under molars have pierced the mucous covering of the 

 jaw. 



The tongue is oblong, and broad at its tip. The oesophagus is rather narrow, 

 but its mucous lining is thrown into many fine, almost lamellar-like folds, which 

 are continued a short way into the stomach along its dorsal wall. 



The stomach of B. pruinosus when dilated shows a tendency to division into 

 four sections. The first occurs to the left of the opening of the oesophagus, and is a 



Fig. 11. — Stomach oi Bhizomijs pruinosus, Blj'th. Nat. size. 



