ISO 



tally: in the Capyhara laterally. The cuneiform process is flat wdth 

 a slight mesial spine : in the Capybara it is convex : in the Beaver 

 hoUowed out like a box. The condyles resemble those of the Ca- 

 pybara, but advance somewhat more forwards. 



" The squamous portion of the temporal bone, which, as is usual 

 in these animals, is separated by a permanent suture from the pe- 

 trous, consists of a narrow strip, advancing from the base of the oc- 

 cipital ridge, and then spreading to form the posterior margin of the 

 orbit ; a bold process backing the posterior angle of the superciliary 

 ridge. The zygomatic process of the temporal bone resembles that 

 of the Beaver more nearly than that of the Capybara or of the Ca- 

 proniys, but turns up at its extremity in a more decided hook. The 

 petrous portion is small, and, with the exception of the ridge round 

 the auditory /orameM, consists of little besides the tympanic bulla, 

 which in the Beaver is externally divided by a strong ridge. 



" The malar bone is elongated and narrow, but, as in Capromys also, 

 it does not advance forwards along the zygomatic process of the max- 

 illary bone as in the Beaver, the suture being just behind the great sub- 

 orbital /bra?ne«. In the Capybara the malar bone does not advance so 

 far. The large foramen alluded to is formed by two branch-lOce pro- 

 cesses of the maxillary bone, the upper one of which arises just below 

 the union of this bone to the frontal, and, bending down, forms the an- 

 terior margin of the orbit ; the other branch arises just over the root of 

 the first molar tooth, and advancing outwards and backwards joins the 

 other branch to form the boundary of the foramen, which is a trian- 

 gular aperture leading at once to the orbit. In the Beaver the sub- 

 orbital /ora»je« is very small. In the Water Rat it is somewhat larger 

 than in the Beaver. In Capromys it is as open as in the Coypus. 



" The lachrymal bone, which in the Capybara spreads largely in 

 a triangle without the orbit at the interior inferior angle, is in the 

 Coypus very small and altogether within the orbit. 



" On turning to the base of the skull we may observe that the 

 internal pterygoid processes, (which in the Capybara are very small, 

 but both in the Beaver and Water Rat largely developed, being in 

 the former of a hook-like figure and touching with their apex the 

 anterior point of the tympanic bulla,) are here moderate and bent 

 back, their points being on a level with the spheno-temporal fissure. 

 The glenoid cavity, which the malar bone contributes to form, resem- 

 bles that of the Beaver. 



" The palate bones, which in the Beaver begin in a point opposite 

 to the posterior edge of the first molar, here begin opposite the pos- 

 terior edge of the third molar ; but they advance further backwards 

 so as to throw the pterygoid processes to a considerable distance 

 from the last molar tooth : in which circumstances the Coypus differs 

 both from the Beaver and the Capybara, and more nearly agrees with 

 Capromys, where the palate bones commence opposite the middle of 

 the second molar, but do not advance so far backwards. 



" The lower jaw of the Coypus is very remarkable ; it seems as if 

 it had been horizontally compressed, so as to throw the broad part 

 of each ramus outwardly into a semilunar shelf. The fact is that 

 this part must be regarded not as the body but as a process of the 



