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 (¢) 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, 7; 
Fig. 43, 2 
