26 THE SKELETON OF THE CAT. 
The sphenoid may thus be described as composed of a central 
portion, the body (a) (basisphenoid), and of two thin expanded 
wings (0) (alisphenoids, ala magne of the human sphenoid); 
each of which has arising from it a thin curved process, the 
pterygoid process (c), directed craniad and largely made up of 
the pterygoid bone. 
The body of the sphenoid (a) lies in the middle line of the 
base of the skull. It is wedge-shaped, with the converging 
sides of the wedge directed laterad and its apex pointed 
craniad. ‘ 
It has six surfaces, of which the dorsal and a part of the 
laterals look into the cranial cavity. The cranial end articu- 
lates with the body of the presphenoid, and the caudal with the 
body of the occipital. 
The dorsal surface is triangular, with one apex of the tri- 
angle truncated, elevated, and directed craniad. This eleva- 
tion is the tuberculum sellz (7). Just caudad of the middle 
the surface presents a rectangular elevation with rounded 
angles, the dorsum sell (¢). The cranial end of the dorsum 
sella presents at each dorsolateral angle a very small smooth 
tubercle which represents one of the posterior clinoid processes 
of man. Between this elevation and the elevated cranial end 
of this surface there is a deep excavation, the sella turcica (/), 
in which in the natural state is lodged the hypophysis. Near 
the cranial end of the sella is a small foramen, probably 
nutrient. At the caudal end of the body a slight notch (jg) 
separates it from the wing: this notch forms a part of the 
foramen lacerum. Against this notch fits the apex of the 
petrous bone, and from it a groove (carotid groove) is con- 
tinued mediocraniad to the sella turcica. 
The ventral surface (Fig. 41, 3) is triangular, smooth, and 
nearly flat; it is marked by a median ridge which is the con- 
tinuation craniad of the ridge on the ventral face of the basilar 
portion of the occipital. | 
Its caudal angles are separated from the rest of the bone 
by sharp triangular elevations, laterad of which are rough 
triangular areas, overlaid when the bones are articulated by a 
triangular spine a“ the tympanic bulla. 
