28 THE SKELETON OF THE CAT. 



The semicircular margin of the bone articulates with the 

 squamous portion of the temporal. At the junction of its 

 caudal and middle third there is sometimes a toothlike projec- 

 tion which underlies the root of the zygoma. 



The whole of the cranial margin, except the lateral end, 

 articulates with the wing of the presphenoid. At this end the 

 angle formed by the junction of lateral and cranial borders is 

 produced into a flat process, which passes dorsocaudad 

 between the squamous portion of the temporal and the frontal, 

 and articulates by the roughened internal surface of its free end 

 with a similar process from the parietal. 



The caudal margin laterad of the groove is bevelled and 

 roughened at the expense of the dorsal surface and is overlaid 

 by the ventral end of the tentorium. Mediad of the groove it 

 projects caudad as a slender point, the lingula of the sphenoid. 

 This is received into a narrow cleft between the apex of the 

 petrous bone and the bulla tympani. 



The pterygoid process (c) is a nearly square, thin plate of 

 bone. The medial surface is smooth and concave, the lateral 

 face is convex and marked by two parallel ridges. The medial 

 one of these is continued craniad from the bony septum which 

 separates the orbital fissure from the foramen rotundum, and 

 the lateral one from the septum which separates the foramen 

 rotundum from the foramen ovale. A sharp triangular spine 

 projects laterad from near the caudal end of the lateral ridge. 



The two ridges and that part of the lateral surface of the 

 bone included between them form a part of the sphenoid bone 

 known as the pterygoid process of the sphenoid bone, in those 

 cases where the pterygoid is a separate bone. 



The remainder of the process is equivalent to the pterygoid 

 bone of other vertebrates. 



Between the caudal margin of this bone and the lateral of 

 the two ridges, i.e., between the pterygoid bone and the 

 pterygoid process of the sphenoid, is a long deep fossa, the 

 internal pterygoid fossa (Fig. 40, s}. The laterocaudal 

 margin of the pterygoid process projects caudad, as a curved 

 triangular spine, the hamulus or hamular process (Fig. 40, /; 

 Fig. 43, /'. 



