Ti6 THE SKULL [chap. 



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

 bounds superiorly a large surface on the side of the skuH, 

 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 

 comparative 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 appearance of the skull, either in mem- 

 bers of the same species, or in different but allied species. 



The upper part of the skull, in front of the diverging 

 boundary lines of the temporal fossa, is expanded and some- 

 what flattened, and has on each side a triangular process 

 {pof), which curves somewhat downwards, and indicates 

 the division of the temporal fossa behind from the orbit 

 in front. This is the postorbital process cf the frontal bone. 

 It is connected by a ligamentous band, in the living animal, 

 with a corresponding process arising from the zygoma ; 

 but when this is removed the orbit and temporal fossa are 

 widely continuous, their respective limits being only in 

 dicated by the above-mentioned processes. 



The face is produced considerably in front of the orbits, 

 and not only becomes more depressed, but also more 

 compressed laterally, and is obliquely truncated anteriorly, 



