ANATOMY OF VERTEBRATES. 



147 



In the Pytlion, figs. 96 and 97, the basloccipltal, i, Is subhex- 

 agonal, broadest anteriorly, smootli and concave above, suturally 

 rough on each side, with a recurved pointed hypapophysis : the 

 hinder facet forms the lower half of the occipital condyle, on eacl 



96 



Section ol tlio Skull of a Python 



side of which is a small sharp process. The basioccipital unites 

 above with the exoccipital, 2, and alisphenoid, f, ; and in front 

 with the basisj)henoid, 5. The exoccipitals (2,2) are each pro- 

 duced backward into a peduncular process supporting a moiety 

 of the upper half of the occipital condyle : at the outer side of 

 the base of the peduncle is an obtuse process, forming the 

 upper part of the ridge continued upon the basioccipital. The 

 outer and fore part of the exoccipital expands, and is perforated 

 by a slit for the eighth pair f>f nerves, articulates l^elow with 

 the basioccipital, is excavated in front to lodge the petrosal 

 cartilage where it articulates with the alisphenoid, and unites 

 above with the superoccii)ital, 3. This is of a subrhomboidal 

 form, sends a spine from its upi)er and hinder surface, expands 

 laterally into oblong processes, is notched anteriorly and sends 

 down two thin plates from its under surface, bounding on the 

 mesial side the surface for the cerebellum, and by the outer 

 side forming the inner and upper parts of the acoustic cavities. 

 The superoccipital articulates below with the exoccipitals and 

 alisphenoids, and in front with the parietal, liy which it is over- 

 lapped in its whole extent. The occipital vertebra is as if it were 

 sheathed in the expanded posterior outlet of the parietal one, the 

 centrum resting on the oblique surface of that in front, and the 

 anterior l^ase of the neural spine entering a cavity in and being- 

 overlapped by that of the preceding neural spine : the analogy of 

 this kind of ' emboitement ' of the occipital in the parietal vertebra 

 with the firm interlocking of the ordinary vertebras of the trunk is 



