FOSSIL REPTILES. 209 



There is no dispute respecting the four parts of the occi- 

 pital which constitute the hinder portion of the head of the 

 crocodile. They are obviously the same as in the young'mam- 

 mifera — only the single condyle, placed under the occipital 

 foramen, appertains entirely to the basilary bone. The upper 

 occipital and the two lateral pieces have also a more important 

 part to play than in the mammifera, because they are hollowed 

 with cavities for the internal ear, for which the os petrosum is 

 insufficient. The same arrangement prevails for the birds, and 

 probably for all the ovipara. 



No difficulty remains but for those parts which, in man, are 

 termed the temporal and sphenoid bones, and for the different 

 pieces into which these bones are dismembered. 



The aldB temporales of the sphenoid are easily recognizable 

 by their position, figure, and function of supporting the central 

 lobes of the cerebrum. It is not surprising to see them form- 

 ing distinct bones, for the same is the case with all the foetuses 

 of mammalia. 



It must be remarked here, that this osseous piece encloses 

 at the same time, and in a single mass of ossification, the ala 

 temporalis, and a great portion of the ala orbitalis. When we 

 examine a fresh crocodile, we find that, if the olfactory nerve 

 and the optic pass between this ala and its corresponding one, 

 the nerves of the third, the fourth, the sixth pair, and the first 

 branch of the fifth, pass through foramina formed in the body 

 itself of the ala, and the assemblage of which, if they were 

 continued, would represent the spheno-orbital cleft. 



The internal pterygoid apophyses of the sphenoid are very 

 obvious, especially when we consider that they not only remain 

 distinct from the body of the bone in many of the mammalia 

 to an advanced age, for which reason they have been named 

 ossa pterygoidea, but that in some ant-eaters they come under- 

 neath, uniting one to another, in concert with the palatine 

 bones, to prolong the nasal tube as far as the basilary region. 

 In the crocodile, even from the foetus state, these pterygoi- 



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