316 EODENTIA. 



contraction of the bodies into a well-marked ridge occurs in these rodents in the 

 sacral region. The sacrum, unlike that of the MuridcB, is very compact and 

 strong, the pleurapophyses being considerably expanded and broadly applied to the 

 ilium. 



In H. badius, Hodgson, only two vertebrae are applied to the ilium, the third 

 vertebra, although assuming the form of a sacral, is quite free and followed by 

 another similar segment ; so that if these two are regarded as pseudo-sacral, there 

 are only sixteen caudal vertebrae. In H. priiinosiis, the third sacral vertebra 

 partially touches the ilium, and is amalgamated posteriorly with a pseudo-sacral 

 vertebral element resembling itself; so that, leaving these out of view, there 

 are 19 caudals. The pseudo- sacral element exists to give support to the thickened 

 base of the tail. In these respects the skeleton of RJdzomys resembles that of 

 Siphneus. 



Broad transverse processes are well developed on the first five caudal vertebrae, but 

 they disappear on the seventh, or are represented by a lateral ridge, as far back as the 

 seventeenth. In R. badius, Hodgson, the transverse processes are distinctly visible as 

 far back as the ninth vertebra, and their rudiments can be traced even to the thirteenth. 

 In both these species, these processes are horizontally expanded. Also in both, the 

 neural canal is perfect on the first four true caudals, and haemapophyses are developed 

 from the sixth to the twelfth vertebra. Metapophyses occur from the first to the 

 fifth caudal, and are well developed. The bodies diminish slightly in length from the 

 first to the fifth caudal, beyond which they lengthen to the ninth, after which they 

 again decrease in length. Eight ribs are directly attached to the sternum, which 

 consists of seven to eight osseous pieces, the last long and narrow, and occasionally 

 amalgamating with the smallest of the segments which immediately precedes it. It is 

 capped by a broad halbert-shaped xyphoid cartilage resembling the manubrium 

 in form. The manubrium at its lower end, and the various segments of the meso- 

 sternum, have each a well-marked epiphysis, and the sternal tips of the rib cartilages 

 are capped with little ossicles in B. badius. The clavicle is strong and slightly 

 outwardly and downwardly curved in its inner half, this head of the bone being large 

 and rounded, while its acromial end expands, and is flattened from above downwards. 

 In one skeleton of M. pruinosus a small ossicle occurs at the sternal end of the 

 clavicle. In B. badius there are only six sternal segments and seven sternal ribs. 

 The manubrium in both species resembles that of SipJineus, and is short and much 

 expanded, so much so that it is broader than long, and is rounded anteriorly ; hence 

 it is very different from the form of this bone in BatJiyergus and Georychus. It 

 has a ventral ridge, rather well marked in one female, but nearly obsolete in a male 

 skeleton. In a female, also, the manubrium is longer than broad, the lower end or 

 shaft being well defined, while in a male it is extremely short— nay, almost 

 absent. Although these two bones are markedly distinct, there can be no doubt 

 of the specific identity of the two sexes, as they were both killed together. 

 The manubrium in a female of B. badius has the same form as in the male 

 of both species. 



