Osteology of the //tW (/ Ilatteiia. 305 



canalis acniiclrcularis frontalis and anteriorly the foramen 

 canali.s seuiicircularis horizontali.s. 



These two foramina are connected together by a cleft or 

 fissura (IM. XIV. ti«2:. 5, x), which divides the upper margin 

 longitudinally into an uj)per and lower half. The cleft at 

 this sjiot has arisen through the aj)j)roximation of the outer 

 and inner lamellaj of the vestibular wall. In addition to this 

 the long transverse cleft in front of the foramen canalis semi- 

 circularis frontalis is also connected by a short cleft, running 

 at right angles to it, with the oval pit, the inosculation of the 

 oriiicium ampullar canalis semicircularis frontalis and the 

 oriHcium canalis semicircularis horizontalis. In no other 

 living lizard is this remarkable phenomenon to be observed. 

 The lower border of the paroccipital exhibits externally an 

 aliform prolongation, and appears, with its lower portion at 

 least, to form tlie ])osterior wall of the cochlea, which is 

 bounded below by the very strongly developed fossa cochlearis 

 of the basioccipital, while exteriuilly it is enclosed by the 

 cartilaginous plate which extends between the paroccipital, 

 otosphenoid, and basioccipital. 



The basisplienoid consists of the body, which constitutes a 

 trapeziform plate of bone, and of the two alary processes. 

 The ujjper concave surface exhibits a median division into 

 two halves by means of a sagittal furrow. This was pre- 

 viously remarked by Baur, who expressed the conjecture {loc. 

 cit.) that the basisphenoid arises from two lateral halves. Oa 

 both sides of this furrow in the anterior third lie two foramina, 

 the orifices of two short canals for branches of the internal 

 carotid. The straight posterior border of the basisphenoid 

 unites with the anterior border of the basioccipital. lieueaih 

 it there project backwards two triangular processes, which 

 attach themselves to the under surface of the basioccipital and 

 with their ends help to form the tubercula sphenooccipitalia. 

 The anterior border, which as dorsum ephippii overhangs the 

 fossa hypophyseos, is deeply indented, so that its two angles 

 become transformed into the processus alares. The two 

 lateral borders converge towards the front and serve to connect 

 the bone with the otosphenoids. 



From tlie anterior portion of the under surface of the basi- 

 sphenoid arise the processus pterygoidei. They are mode- 

 rately long, inclined somewhat forwards, and diverging at 

 the ends, on the outer sides of which lie the articular surfaces 

 for connexion with the pterygoids. 



Between the processus pterygoidei arise the fairly long 

 cylindrical processes for the inferior trabecule ; they are 

 separated by a furrow, which ends posteriorly in the shape of 



