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 (b) (alisphenoids, alae magnae 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 sellae (d). Just caudad of the middle 

 the surface presents a rectangular elevation with rounded 

 angles, the dorsum sellae (c). The cranial end of the dorsum 

 sellae 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 (g) 

 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 from the tympanic bulla. 



