128 



moveable ribs, but no hypapophyses ; and of the 70 caudal vertebrae, 62 have 

 hypapophyses in pairs. Mus. South. 



626. The neural arches of the occipital, parietal, and frontal vertebrae of a large 



Python. 



From the back part of the cranium a longitudinal vertical section has been removed, to 

 show the thickness and density of the walls of that cavity, and the mode in which the occi- 

 pital arch is wedged into the posterior expanded part of the parietal one, analogous to that in 

 which the neural arches of the trunk are interlocked together. The long and slender colu- 

 melliform stapes is preserved in this specimen. The numbers on the bones indicate their 

 names according to Table I. of SYNONYMS. 



The exoccipitals meet above the foramen magnum. . The paroccipital is an exogenous 

 process. The petrosal is quite excluded from the cranial cavity, the otocranial plates of the 

 exoccipital, alisphenoid and superoccipital bones uniting by a triradiate suture. Ossification 

 extends from the frontal into the neurapophysial walls of the prosencephalic cavity, and is 

 continued from below inwards and upwards so as again to join the upper plate of the frontal, 

 forming a septum at the fore part of the cranial cavity, like an ossified falx, and completely 

 surrounding the part through which the rhinencephalon is continued. The unusual strength 

 of the cranial parietes, and the tile-like imbrication of one thick and dense bone over another, 

 relate to the requisite provision of unusual resistance against the numerous causes of injury to 

 which a creature doomed to crawl along the surface of the earth is liable from falling bodies, 

 blows, and the heavy tread of large quadrupeds. 



Presented by Prof. Owen, F.R.S. 



627. The tympanic, pterygoid and transverse bones of the same Python. 



Presented by Prof. Owen, F.Ji.S. 



628. The disarticulated bones of the skull of the Tiger Boa (Python tigris). They 

 are numbered according to Table I. of SYNONYMS. 



In studying the osteology of the head of the Python, as the type of the Ophidian Order, 

 by the aid of the following description, the student should compare the disarticulated skull 

 with that of the large skeleton, No. 602. 



The basioccipital (i) is subdepressed, broadest anteriorly, subhexagonal ; smooth and con- 

 cave at the middle above, with a rough sutural tract on each side ; and a hypapophysis below, 

 produced into a recurved point. The hinder facet of the basioccipital is convex, forming the 

 lower half of the occipital condyle : the two lateral borders are defined by a produced angle : 

 the front facet forms a straight transverse sutural surface for the basispheuoid. The articular 

 tubercle is supported on a short peduncular prolongation, on each side of the base of which 

 there is a small sharp process. The basioccipital unites above and laterally with the exocci- 

 pitals and alisphenoids, and in front with the basisphenoid, upon which it rests obliquely, and 

 it supports the medulla oblongata on its upper smooth surface. 



