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 apparent 
that this cavity will be more or less complete, according 
to the degree of development of these bones ; but this 
cavity 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 cranium, 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 backwards, to form, in conjunction with the infe- 
rior occipital, that long hook analogous to the inferior 
spinous processes of the vertebrse, 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 in front, and descend 
in the orbits to unite with the sphenoid. 
4. The oceipitals, 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 
