395 



cesses of the lower jaw are subequally developed, are slender, and pointed. A postorbital 

 ridge is developed from the fore part of the expanded plate of the squamosal, as in the On- 

 datra. 



Presented by William Clifl, Esq., F.R.S. 



2209. The skull of the Water Vole (Arvicola amphibia). 



Presented by Henry Cline, Esq. 



2:210. The upper jaw of the Water Vole (Arvicola amphibia}, in which, from some 

 accident to the lower jaw, the incisors have not been opposed, and have con- 

 sequently grown to an unusual length, and are curved and pointed. 



Presented by Sir Joseph Banks, P. U.S. 



The following are parts of the same skeleton of the Water Vole (Arvicola, amphibia). 



Hunterian. 



2211. A mutilated cranium. 



The canal is laid open which leads from the crescentic orifice at the fore part of the ant- 

 orbital aperture into the lower part of the nasal meatus, above the prepalatine fissures. 



2212. The two rami of the lower jaw. 



2213. The atlas. 



The transverse process is perforated both horizontally and vertically by the vertebral artery, 

 which afterwards perforates the neural arch. This is also perforated behind by the second 

 pair of spinal nerves. The atlas consequently presents four distinct foramina on each side 

 of the ' foramen magnum,' or neural canal. 



2214. The remaining cervical vertebrae, with the bones of the trunk and tail. 



The dentata and third cervical have each two tubercular hypapophyses. The first free 

 or ' dorsal ' rib is very securely articulated by its head to the interspace between the last cer- 

 vical and first dorsal, by its tubercle to the ends of the diapophyses of the same two verte- 

 brae, and by the under part of its neck to the pleurapophysis of the sixth cervical vertebra. 

 The potential base of the accessory processes progressively expands above the diaponhyses of 

 the dorsal vertebrae as far as the tenth, and divides in the eleventh, the metapophysis and 

 anapophysis being quite distinct on the twelfth. The anapophyses disappear in the last lum- 

 bar vertebrae. Thirteen pairs of ribs are here preserved, and the seven anterior pairs directly 

 join the sternum, which consists of six bones, the last being unusually long and slender, and 

 supporting a xiphoid cartilage. Five vertebrae are anchylosed to form the sacrum, and there 

 are '21 caudal vertebrae. The iliac bones articulate exclusively with the first of the sacral 

 series. The clavicles, with the two episternal ossicles, are preserved in connection with the 

 manubrium stemi. 



3 E 2 



