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, e, 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, d] ; it 

 marks the point of beginning ossification. An obscure curved 

 ridge (Fig. 39, e), 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 3') 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 \vith 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, /) 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, /) 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 fossae 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. 



