304 Herr F. Siebenvock on the 



tions. On the inner wall of the roof of the vestibular portion 

 lies the inosculation of the commissure of the canalis semi- 

 circularis frontalis and the canalis semicircularis sagittalis, 

 and in front of this at the lower margin of the inner wall the 

 orificium internum of the aqueductus vestibuli. At the upper 

 external margin of the vestibular portion the foramen canalis 

 semicircularis frontalis is visible, while the foramen canalis 

 semicircularis sagittalis lies away towards the middle of the 

 lateral border of the supraoccipital at a distance from the 

 vestibular portion. This aperture is otherwise usually found 

 in lizards at the anterior circumference of the vestibular 

 portion. On the upper surface of the supraoccipital neither 

 canal is noticeably visible ; the sagittal canal stands out on 

 the inner surface pretty distinctly. 



The paroccipital, which in young individuals constitutes an 

 independent bone, has some similarity to a spoon, for it is 

 strongly arched and sends off outwards a long process, the 

 processus paroticus. The paroccipital forms the posterior 

 wall of the bony labyrinth, and unites with the otosphenoid in 

 front, with the supraoccipital above, and with the basioccipital 

 below. To the posterior wall is attached the upper end of 

 the pleuroccipital, while the lower end of this, which as pars 

 condyloidea unites with the basioccipital, forms with the 

 posterior wall of the paroccipital the incisura vena? jugularis 

 and is completed with the basioccipital to form the foramen 

 jugulare. From the anterior external border, which is exca- 

 vated in the shape of a semicircle and forms the incisura 

 foraminis vestibuli, arises the processus paroticus. This is 

 long, strongly compressed, hollowed out in the shape of a 

 groove in front for the accommodation of the columella auris, 

 and directed horizontally and somewhat backwards. The 

 anterior excavated surface of the paroccipital forms the hinder 

 portion of the vestibulum. It is divided into the outer 

 portion, which extends in the shape of a crescent from above 

 downwards, and the inner, smaller, but very deep portion, 

 the posterior ampullary chamber, which forms an oval pit and 

 at the bottom contains two holes, the oriticium ampulUe canalis 

 semicircularis frontalis above and more towards the rear, and 

 the orificium canalis semicircularis horizontalis below and 

 more towards the front. The vestibulum in llatteria conse- 

 quently possesses one hole less than in the majority of lizards, 

 in which the two oritices just mentioned, divided by a septum, 

 open into the vestibulum, while in llatteria they fuse together 

 into one large oval hole. At the upper margin of the vesti- 

 bular cavity, to which the supraoccii)ital is attached behind 

 and the otosphenoid in front, we tind po:steriorly the foramen 



