ix.] OF THE DOG. 135 



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 distinctly marked off laterally by 

 ridges, which, commencing in the median line above, runs 

 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 

 lambdoid or occipital crest. They are far more conspicuous 

 in old than in young animals. 



The superior surface of the skull (Fig. 48) may be divided 

 into a cranial and facial portion. The former is of a some- 

 what oval form. On its upper surface posteriorly, in full- 

 grown dogs, is a median ridge joining behind with the 

 superior angle of the occipital crest, and dividing anteriorly 

 into two less elevated ridges which curve outwards to the 

 superior posterior angle of the orbit. This ridge, as long as 

 it is single and median, is called the sagittal crest. It bounds 

 superiorly a large surface on the side of the skull, limited 

 behind by the occipital crest, and below by the zygoma, 

 called the '' temporal fossa," from which the temporal muscle 

 takes its origin. In young dogs the upper boundary of the 

 surface for the origin of this muscle is of less extent, not 

 reaching so high as the middle line of the cranium, and is but 

 obscurely indicated on the comparatively smooth surface of 

 the skull. As the muscle increases in development its surface 

 of origin gradually ascends until it reaches the middle line, 

 and with advancing age a still larger space is afforded for it 

 by the gradual growth of the sagittal crest. 



These changes in the upper part of the skull during growth 

 have been particularly noticed, because they take place in very 

 many animals, and, without altering in the least the actual 

 form of the brain-case give rise to a very different external 



