NECTURUS MACULATUS. 



415 



rate. The first two receive between them the parietal process of the frontal, and the 

 antero-lateral one, which is much the larger, reaches the olfactoiy region and assists in 

 the formation of the olfactory foramen. This process bears upon its ventral .side a large 

 portion of the orbito-sphenoid process. The quadrate process is small and fiat, and pro- 

 jects over that part of the (luadrate cartilage designated above as the "istlunns.y The 

 outline of the posterior portion is practically a square, of which the two cniter corners are 

 obviou.s, the posterior one being considerably prolonged. These may be termed respec- 

 tively the pro-otic and opisthotic processes in reference to the bones which they partially 

 overlap. This portion forms a thin outer covering for the otic capsule and corresponds to 

 it in shape, being convex above and concave beneath. It forms the otic fossa of the ven- 

 tral sui'face. 



There are several prominent muscular ridges upon the dorsal surface of the parietal, 

 the most important of which are several irregular ones upon the posterior portion and a 

 median one formed between the two bones and prolonged into a median intermuscular 

 septum. 



o. PARABASAL. This is the flattest and mo.st extensive bone of the skull and forms 

 nearly the whole of the floor 

 of the brain case, and at the 

 same time the roof of the 

 mouth. It is nearly in the 

 shape of a parallelogram with 

 rounded corners, but is a little 

 broader in the otic region 

 and becomes somewhat nar- 

 rowed anteriorly. It is al- 

 most without special features 

 otiier than the impressions 

 made by the Ixjnes which 

 come in contact with it, the 

 frontals and parietals upon its 

 dorsal, and the vomers upon 

 its ventral surface. Upon 

 the dorsal surface at the 

 posterior end there is a pair 

 of low latei'al ridges which 

 reinforce the orbito-sphenoid 

 processes of the parietal and 



VENTRAL 



Fig. l.i. Two views of the parabasal taken from different individuals. The 

 view of the dorsal side is 4 times enlarged, that of the ventral, being from a 

 much larger individual, but 24. Contact surfaces with other bones are desig- 

 nated by an .\. 



