388 



2158. The skull of a Canada Beaver (Castor canadensis). 



It is of a mature animal, with the permanent teeth fully acquired. The temporal ridges 

 have met upon the parietal bones, and have developed a low crest along the interparietal, and 

 a higher transverse occipital crest. The tympanic extends outwards and curves forwards and 

 a little upwards : the perforation in the squamosal between the tympanic and zygomatic 

 processes is retained and well marked. The perforations between the superoccipitals and 

 mastoid are less distinct. Both paroccipital and mastoid processes are distinctly, but not 

 excessively developed. 



Presented by Henry Cline, Esq. 



2159. The skull of a Canada Beaver (Castor canadensis). 



The thin plate of the basioccipital, which forms the roof of the depression in that bone, 

 appears to have been absorbed in some parts. The long hamular process of the pterygoids 

 articulates with the rough process of the petrosal. A ridge is continued from the tubular 

 tympanic upon the outer side of the petrosal bulla. 



Presented by Sir John Richardson, M.D., F.R.S. 



2160. The skull of a Canada Beaver (Castor canadensis). The nascent premolar has 

 begun to appear on the left side of the upper and lower jaws. 



Presented by Henry Cline, Esq. 



2161. The cranium of a Canada Beaver (Castor canadensis). The nasal bones have 

 been removed, and a line drawn between the antorbital tubercles, showing its 

 relation to the hinder ends of the nasals. The foramen between the super- 

 occipital and mastoid is large, while that between the orbitary and zygomatic 

 processes of the squamosal is very small in this skull. Hunterian. 



2162. The anterior part of the cranium of a young British Beaver (Castor europaus 

 C. fiber, Linn.). The nasal bones have been removed, and a line drawn 

 between the antorbital tuberosities, showing the greater extent to which the 

 nasal bones are extended beyond such line. This osteological character of the 

 European species is constant, and serves to distinguish the skull from that of 

 the Canada Beaver. Presented by Prof. Owen, F.H.S. 



2163. A portion of the skull of a young Canada Beaver (Castor canadensis), with 

 the teeth removed from the left side of the upper and lower jaw, and sepa- 

 rately displayed. 



The first of the molars is the deciduous one, and the germ of its successor may be dis- 



