148 HIGH SCHOOL ZOOLOGY. 



the skull of a cat with that of a lower Vertebrate is the relative 

 l)ro})ortion of the cranium to the face. Here it is obvious that 

 the facial bones form only a small portion of the skull, the in- 

 creased size of which, on the other hand, is chiefly due to the large 

 surface of the frontal, parietal and squamosal bones which form 

 the greater part of the brain case. A second feature is the 

 widely-arched foi-m of that bar (zygomatic or jugal), which ex- 

 tends from the articulation of the lower jaw to the superior max- 

 illa, and is, therefore, comparable to the quadrato-jugal bar of the 

 reptiles. It is widely arched, partly to accommodate under- 

 neath it the great temporal muscle, which arises in the temporal 

 fossa bounded behind by the strong lanibdoid crest, and ])artly 

 to give a wider origin to another muscle of mastication which 

 arises from its convex outer surface, the masseter. A third 

 feature is the tendency to union of certain groups of bones sepa- 

 rated by sutures in the reptiles ; thus the mammalian occi})ital 

 bone is formed of the four occij)ital elements and rests on the 

 atlas vertebra by two condyles which are borne on the exoc- 

 cipitals ; it likewise absorbs in older animals an unpaired 

 interparietal^ which is wedged between the supraoccipital and 

 the parietals. Tlie mammalian temporal bone is similarly com- 

 plex, because it embraces not only the three periotic bones* 

 with the tympanic and squamosal, but probably also the quad- 

 rate and quadrato-jugal. Within the bullate tympanic is to be 

 found the chain of small bones answering to the columella 

 auris of the reptiles. A third com[)lex bone is the sphenoid, 

 the elements of which, however, are more easily separated from 

 each other. They are the basi-, pre-, ali- and orbito-s[)henoids 

 with the pterygoids. Finally the ethmoid, which looks into the 

 skull with its perforated plates, into the nasal cavity with the 

 septum and the labyrinthine turbinals, and into the orbits with 

 its orbital plates, is formed of mesethmoid and ])areth molds. 



Attention should also be directed to the following points : — 



