397 



Family Murida. 

 Genus Mm. 



Dental formula : t rj, p }, m |^|= 16 : molars rooted.. 



2223. The skeleton of a large male Black Rat (Mus Eattus). 



The vertebral formula is : 7 cervical, 13 dorsal, 6 lumbar, 3 sacral, and 30 caudal. Seven 

 pairs of ribs directly articulate with the sternum, which consists of six bones. The spine of 

 the second dorsal is much elongated, and its apex is a detached epiphysis. The spine of the 

 tenth is that towards which the spines of the other trunk-vertebrae converge. The accessory 

 process, commencing in the sixth dorsal, divides into the metapophysis and anapophysis in 

 the ninth dorsal : the anapophyses are obsolete in the last two lumbar vertebrae. The cla- 

 vicles are slender, but are complete. The deltoid ridge is angular, and commences near the 

 upper end of the humerus, which is imperforate at the lower extremity. A strong ridge 

 represents the third trochanter of the femur. There is a fabella behind each condyle. The 

 distal portion of the fibula coalesces with the tibia. 



Mus. Brookes. 



2224. The partially articulated bones of the skeleton of the female of the Black Rat 

 (Mus Rattus}. 



The vertebral formula is : 7 cervical, 19 dorsal and lumbar, 5 sacral and 32 caudal. 



Mus. South. 



2225. The skeleton of the Norway Rat (Mus decumanus). 



The vertebral formula is : 7 cervical, 1 2 dorsal, 7 lumbar, 3 sacral, and 22 caudal, but 

 the end of the tail is incomplete in this skeleton. The spines of both the first and second 

 dorsal vertebrae are here elougated, and a semiossified cartilaginous epiphysis is articulated to 

 the summit of both. This species differs from the Black Rat chiefly in its relatively shorter 



tail. 



Presented by Robert Willis, M.D., F.fi.S. 



2226. The skeleton of a female Norway Rat (Mus decumanus). 



The vertebral formula is : 7 cervical, 13 dorsal, 6 lumbar, 4 sacral, and 28 caudal. 

 In all these skeletons of the Rats, the tubercle of the first rib articulates with the diapo- 

 physis of the last cervical as well as with that of the first dorsal. 



Presented by Henry Cline, Esq. 



2227. The skull of a Norway Rat (Mus decumanus}. 



The upper surface of the cranium bends very slightly from the straight line in its extent 

 from the superoccipital crest to the end of the nasal bones. There is a broad interparietal : 

 the sides of the parietals bend down almost at a right angle with the nearly flat upper sur- 



