in.] THE CRANIAL SKELETON. 97 



here it may be stated that the division of it adopted in human 

 anatomy, into cranium and face, is one which is natural. By 

 the former we shall understand the brain-case proper, and no 

 more. By the face we shall understand not only the bones 

 usually included in that category in anthropotomy, but the 

 ethmoid and parts of the sphenoid also, namely the internal 

 pterygoid processes, which, as we have seen, arise in man 

 about the second visceral arch. 



The number of bones of which the skull is composed in 

 man when adult is much less than in many animals ; on the 

 other hand, it is more than in many, where, as in the class of 

 Birds, the process of anchylosis is more rapid and extensive. 



Certain small bones of the ear, called auditory ossicles, 

 are, in works on human anatomy, included in the description 

 of the internal ear. For this reason the full notice of these 

 ossicles will here also be similarly deferred ; though from the 

 important part they are said to play in many lower, and all 

 the lowest forms, and their relations to hyoidean structures, 

 they must be somewhat noticed even in describing the true 

 skeleton considered as the framew y ork of the body. 



19. The OCCIPITAL bone of man represents some of the 

 most constant ossifications of the solid cranium. The con- 

 dition of union its parts present in him is the one normal in 

 his class, though the union of its elements is often longer 

 delayed in some Mammals than in him. 



On the other hand, the occipital bone (or parts of it) may 

 anchylose with more than it anchyloses with in man, as is 

 the case in the Sauropsida, where, except in the Chelonians, 

 two portions of the petrous bone (the epiotic and opisthotic) 

 become intimately united with parts of the occipital. 



In the lower forms (or Ichthyopsida), where the skull is 

 ossified, either the main parts of the human occipital are 

 represented by distinct bones, or only a portion of them are 

 so represented. 



Thebasilar process (basi-ocdpitaT) is a constant ossification 

 in all except Batrachians and some Fishes, and when y 

 in the latter (as the Cod. Perch, Pike, c.), remains a distinct 

 bone throughout life. It may, however, as in Batrachians 

 and in the Lepidosiren. be represented merely by cartilage ; 

 and this in spite of other portions of the occipital being 

 ossified. The basi-occipital may give origin to a median 

 descending process like a hypapophysis, and may indeed (as 

 in the Carp) send one down so far as to penetrate the watt 

 of the alimentary canal and serve in mastication. 



H 



