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 olfactory 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 flat, and pro- 
jects over that part of the quadrate cartilage designated above as the “isthmus.” The 
outline of the posterior portion is practically a square, of which the two outer corners are 
obvious, 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 surface. 
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. 
3. PARABASAL. ‘This is the flattest and most 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 
Position 
of . . 
trabecule. 3 i 
rounded corners, but isa little 
broader in the otic region 
and becomes somewhat nar- 
rowed anteriorly. It is al- 
most without special features 
other than the impressions 
made by the bones which 
come in contact with it, the 
frontals and parietals upon its 
dorsal, and the vomers upon 
a YN 
? Area in QE 
lm dcgntane = 
its ventral surface. Upon Exo 
the dorsal surface at the DORSAL 
VENTRAL 
posterior end there is a pair 
. : Fig. 15. Two views of the parabasal taken from different individuals. The 
of low lateral ridges which 4 
view of the dorsal side is 4 times enlarged, that of the ventral, being from a 
reinforce the orbito-sphenoid much larger individual, but 24. Contact surfaces with other bones are desig- 
processes of the parietal and nated By, a2, 
