114 THE SKULL [chap. 



the foramen lacerum posterius (between the auditory bulla 

 and the exoccipital), and transmits the internal carotid artery. 

 This vessel appears again on the surface, at the anterior 

 extremity of the bulla, close to the Eustachian orifice ; then 

 runs upwards and inwards and enters the cranium through 

 the foramen lacerum medium. 



This completes the enumeration of the bones of the 

 cranium. Before proceeding further, it will be desirable 

 to take a general survey of this part as a whole, pointing 

 out the most prominent features of its various surfaces. 



The posterior sitrface is, in a general sense, a vertical 

 wall, somewhat triangular in form, broad below and pointed 

 above. In the middle line, at its lowest border, is the nearly 

 round foramen magnum^ bounded by the supraoccipital 

 above, the exoccipital s on each side, and the basioccipital 

 below. On the sides of the foramen magnum, and 

 approaching each other in the middle line below, but 

 diverging above, are smooth eminences, the occipital 

 condyles. Further outwards, and separated from these by 

 a deep valley, are the paroccipital processes, projecting 

 backwards and downwards. Outside of the upper part or 

 origin of these processes, the mastoid portion of the periotic 

 appears on the hinder wall of the skull. The remainder of 

 the region is formed by the supraoccipital, and it is dis- 

 tinctly marked off laterally by ridges, which, commencing 

 in the median line above, run downwards and outwards, 

 at the junction of the parietals and supraoccipital, and are 

 continued on the squamosal in front of the mastoid to the 

 upper edge of the external auditory meatus. The ridges 

 of each side taken together form the lajuhdoid or occipital 

 crest. They are far more conspicuous in old than in young 

 animals. 



