192 THE SKULL [CHAP. 



large post-glenoid and post-tympanic processes ; the latter 

 joins the paroccipital process of the exoccipital, but above 

 their point of union a narrow slip of the mastoid appears 

 on the surface of the skull. The periotic is not ankylosed 

 to the squamosal or to the tympanic, which is exceedingly 

 rudimentary, forming a small irregular floor to the tympanic 

 cavity, with an oval lip for the attachment of the membrana 

 tympani, and always becomes detached in macerated skulls. 



The mandible is chiefly noticeable for the great rounded 

 incurved posterior projection of the angle. 



The hyoid has a simple, elongated stylohyal without pos- 

 terior process at the upper end, but one other ossification in 

 the anterior cornu, and no glossal process to the basihyal. 



Sub-Order Artiodadyla. The skull of the Sheep, as one 

 of the best known and easily procurable examples of this 

 group, may be first described, though in some respects it 

 is rather peculiarly modified. 



On comparing the section of the cranium (Fig. 62) with 

 that of the Dog, it will be seen that there is a great difference 

 in the relation of the principal elements to each other, inas- 

 much as the face is bent downwards on the basicranial axis, 

 so that when the latter is horizontal, the upper surface of 

 the face looks forwards and the palate backwards. The 

 occipital foramen is terminal posteriorly, the tentorial plane 

 nearly vertical, so that the cerebellar fossa is altogether 

 behind the cerebral, but the plane of the cribriform plate 

 is horizontal, and the olfactory fossa altogether beneath the 

 anterior portion of the cerebral fossa. 



The occipital region is small and sloping forwards. 

 There are long paroccipital processes (//). In very young 

 skulls a distinct interparietal bone is present, but in the 

 specimen figured this has coalesced with the supraocci- 

 pital (SO). The two parietals (Pa) unite very early at the 



