394 



bone ; but the turbinal bones appear at the fore part of the orbit between the two processes 

 of the maxillary which join the frontal, and above the aperture communicating with the nasal 

 cavity. The anterior part of the maxillary, in front of the antorbital foramen, is swollen, and 

 forms a curved canal commencing by an oblique aperture superiorly, and descending outwards 

 and backwards round the socket of the superior incisor to terminate in the nasal meatus : 

 this part may, probably, protect the lacrymal sac and duct. The interparietal is a trans- 

 versely quadrate bone. The sagittal suture is retained, and the upper surface of the parietal 

 is smooth, and nearly flat : the temporal ridges meet and develope a crest upon the narrow 

 frontals, obliterating the frontal suture. The back part of each ramus of the lower jaw is 

 trident-shaped from the almost equal development of the coronoid and angular processes, on 

 each side the base of the narrow process supporting the condyle. The molar teeth are re- 

 markable for their alternately disposed triangular lobes. 



Presented by Henry Cline, Esq. 



2206. The skull of an Ondatra (Fiber zibeticus}, with the teeth removed from the 

 right side of both upper and lower jaws, and separately displayed. 



It is smaller than the preceding specimen, and is probably the skull of a female. 



Hunterian. 



2207. The upper and lower jaws of the Ondatra (Fiber zibeticus), with the teeth 

 from the left side of the upper and from the right side of the lower jaw 

 displayed. 



Short roots have been developed from the grinding teeth. These consist of the premolar, 

 p 4, and first and second true molars, m 1, m 2, on each side of both jaws. The premolar is 

 the largest, especially in the lower jaw, where it presents six lobes on the inside and five on 

 the outside of the crown. 



Hunterian. 



Genus Arvicola. 

 Dental formula : i j^jj, p |^|, m ^5= 16. 



2208. The skull of the Water Vole (Arvicola amphibia). 



The foramen magnum is triangular and pointed above. The paroccipitals are more deve- 

 loped than the mastoids. The occipito-mastoid foramina are small. The squamosal perfo- 

 ration is large. The interparietal is a transversely quadrate bone. The temporal ridges meet 

 upon the compressed frontal, but do not develope a crest. There is no trace of lacrymal bone. 

 The, probably lacrymal, canal on the fore part of the maxillary curves round the outside of 

 the socket of the incisor, as in the Ondatra, but is less swollen. The zygomatic process of 

 the maxillary does not extend so far backwards as in the Ondatra. The interorbital septum 

 is entire. The turbinals are exposed anterior to the orbits. The angular and coronoid pro- 



