359 



enormous length. The basioccipital contributes to each condyle its lower extremity. The 

 exoccipitals very nearly meet above the foramen magnum, the plane of which is nearly 

 vertical. The squamosals are distinct, and essentially like those in the Hare, sending back- 

 wards the long compressed lamina which clamps the tympanic and mastoid to the side of the 

 cranium. A venous sinus issues from beneath this process of the squamosal. The longi- 

 tudinal groove forming the articular cavity for the lower jaw at the base of the zygoma is 

 more angular than in the Dolichotis, and is completed externally by the malar bone. The 

 meatus auditorius is unusually contracted, is cleft below, and bounded there by two small 

 tuberosities. The temporal and orbital fossae are blended together. The lacrymal bone is 

 of unusual size, and extends forwards upon the side of the face between the frontal and 

 maxillary. The antorbital vacuity is immense. The nasal processes of the maxillary present 

 a shallow depression. The nasal bones are long, large, and of nearly equal breadth through- 

 out. The nasal processes of the premaxillaries are coextensive with them. The sagittal suture 

 is obliterated, as well as a great part of the frontal suture. There is no trace of interparietal 

 bone. There is a single foramen incisivum situated anterior to the two large normal pre- 

 palatine apertures ; the postpalatine foramina are in the centre of the bony palate, between 

 the palatines and maxillaries. The palatines are large. The lower jaw shows a strong ridge 

 or platform outside the molar alveoli. The coronoid and condyloid processes rise very little 

 above the grinding surface of the molars. The chief process of the lower jaw is the angle, 

 which is broad, compressed, and produced far backwards, where it terminates obtusely. 

 The upper surface of the skull is flat, and its contour deviates little from a straight hue, 

 slightly descending towards the occiput and towards the ends of the nasals. The zygomatic 

 arch is compressed but deep, especially below the fore part of the orbit. The acoustic bullae 

 are comparatively small. The incisors are longitudinally grooved along their convex sides. 



Purchased. 



1975. The skull of a smaller Capybara (Hydrochoerus Capybara), with the mature 

 dentition. 



The teeth have been removed from the right side of the upper and lower jaws and are 

 separately displayed. The scalpriform incisors show the characteristic curvature and equable 

 size from the exposed to the implanted extremity, the latter of which is deeply excavated by 

 a large conical cavity, which contained the persistent pulp. The enamel is partially disposed 

 along the outer or convex half of the tooth, and so maintains a sharp edge on the exposed and 

 abraded extremity. These are characteristics of the incisors common to the entire Order. 

 The longitudinal groove which indents the enamelled surface of both upper and lower incisors 

 is peculiar to a certain number of the Rodentia with the Capybara : the molar teeth show in 

 a well-marked degree the transverse direction of the enamel plates, which renders their action 

 most efficacious in the grinding movements of the lower jaw backwards and forwards, to 

 which directions the peculiar form of the glenoid articular surfaces almost restricts it. The 

 molar teeth are four in number on each side of both jaws ; the first displacing a deciduous 

 molar is thus shown to be a premolar : it resembles in structure the two succeeding molars in 

 the upper jaw, and consists of two plates of dentine, each of which is bent lengthwise upon 



