OF THE BONES OF THE HEAD. 31 



or less drawn out, opened out at the base, dilated in the 

 middle, and thickest towards the extremity. The sides 

 of this part serve for the attachment of the temporal 

 muscles, the action of which, in old animals, produces a 

 projecting crest on the summit of the cranium. The 

 temporal fosse, thus formed, is behind indistinctly bound- 

 ed by the tympanites ; before are the posterior frontal 

 bones, which, when they exist, indicate the limits between 

 that cavity and that containing the eye. It is aj^parent 

 that this cavity will be more or less complete, according 

 to the degree of development of these bones ; but this 

 ca\'ity is never entirely closed, except at its anterior part. 

 The nasal cavity too, always open to the front, and with 

 its internal apertures very near the end of the snout, 

 occupies the anterior part of the cranium, and is very im- 

 perfectly covered by the nasal bones. 



The osseous pieces, composing the walls of the cavity of 

 the cranium, are all firmly united, and consist of the fol- 

 lowing : — 



1. The sphenoid, a pairless bone of a lengthened form, 

 occupying the base of the cranimn, and provided on each 

 side, in many serpents not venomous, especially in the 

 Boa, with a small protuberance or projection, which serves 

 for the attachment of the internal pterygoid bone ; on the 

 other hand, in venomous snakes, properly so called, its 

 posterior part is contracted to a crest, which is often pro- 

 longed back\vards, to form, in conjunction with the infe- 

 rior occipital, that long hook analogous to the inferior 

 spinous processes of the vertebraB, and which presents a 

 powerful lever, acting as a point of insertion for the flexor 

 muscles of the head. 



2. The parietal, also a pairless bone, which chiefly de- 

 termines the form of the posterior part of the head, of 

 which we have, therefore, already mentioned the form. 



3. The frontals, properly called, bones always in pairs, 

 which terminate the cranial cavity m front, and descend 

 in the orbits to unite with the sphenoid. 



4. The occipitals, divided into inferior and superior, in- 

 dented at the posterior part of the cranium, and fortified by 

 several protuberances, of which those surrounding the oc 



