36 THE SKELETON OF THE CAT. 
Parietal Bone. Os parietale (Figs. 39, 40, and 43, 3).— 
The parietal bones form the larger part of the lateral and dorsal 
boundary of the cranial cavity. Each is a thin rectangular 
bone, compact and curved and with a deeply notched shelf of 
bone, the tentorium (Fig. 42, ¢, and Fig. 43, /), projecting 
inward from near the caudal margin. 
The outer surface is smooth and convex. The highest part 
of the convexity, a little caudad of the middle of the bone, is 
known as the parietal tubercle or eminence (Fig. 39, @); it 
marks the point of beginning ossification. An obscure curved 
ridge (Fig. 39, ¢), running from the caudodorsal angle or a 
point craniad of it craniolaterad, indicates the boundary of the 
origin of the temporal muscle. Near the ventral border the 
surface is roughened and is covered in the natural state by a 
part of the squamous portion of the temporal bone. 
The inner surface (Fig. 43, 3 and 8) is smooth and marked 
by ridges and grooves for the convolutions of the cerebrum. 
Near the medial border is a ridge which, when the bone is 
articulated with that of the opposite side, forms a shallow groove 
for the superior sagittal sinus. Beginning near the middle of 
the ventral margin and passing dorsad is a groove for the 
middle meningeal artery. The tentorium (Fig. 43, 7) arises 
from the inner surface near its caudal margin and projects 
mediad as a thin curved or notched shelf of bone which 
separates the cerebellar fossa (Fig. 43, 7) of the cranium from 
the cerebral fossa (Fig. 43, //). When the parietals are 
articulated there is left between the tentoria a large foramen 
by means of which the two fosse communicate. The. foramen 
is bounded laterally and dorsally by the free margins of the 
tentoria, while the ventral end of each tentorium articulates 
with the alisphenoid, and its dorsal end with the opposite ten- 
torium. 
The medial border is straight and is united by suture to the 
opposite bone. ; 
The cranial border is bevelled at the expense of the inner 
surface and articulates with the frontal. Just ventrad of the 
middle of the border projects a sharp spine which fits into a 
corresponding notch in the caudal border of the frontal. 
