250 



MAMMALIAN ANATOMY 



The anterior sphenoid is composed of the median unpaired pre- 

 sphenoid and the lateral paired orbitosphenoids. It is so covered 

 below by the palatines and pterygoids that only a narrow median strip 

 of the presphenoid is visible on the under surface of the skull (Fig. 

 137). Each orbit osphenoid is seen in the posterior lower part of the 

 orbital cavity above the alisphenoid and in front of it, below the 

 frontal, and behind and above the palatine (Fig. 183). The upper 

 surface of the anterior 'sphenoid is wholly visible at the anterior part 

 of the bottom of the cranial cavity, where it forms all the floor of the 

 olfactory fossa and the middle part of the floor of the anterior cerebral 



FIG. 181. 



With Ethmoid. 



'ith Frontal. 



Presphenoid. 

 Orbitosphenoid. 



Optic Foramen. 



Anterior Clinoid Process. 



Sella Turcica. 

 Foramen Rotundum 



Posterior Clinoid, Process. 



Foramen Orale. 



Groove for Cavernous Sinus. 



Basisphenoid. 



With Parietal. 



Groove for Vidian Nerve. 



- With Temporal. 

 Alisphenoid. 



With Tentorium with Basioecipital. 

 of Parietul. 



THE SPHENOID BONE, CRANIAL OR UPPER ASPECT. 



fossa (Fig. 206). Inasmuch as the orbitosphenoids are always found 

 firmly united to the presphenoid and cannot be clearly defined, it will 

 be more satisfactory to describe the anterior sphenoid as a single part. 

 That portion, however, which may be considered the presphenoid 

 is seen only on the upper and the under surface. It is six-sided, and 

 twice as long as wide. In front it is almost as high as wide, but at 

 about the junction of the middle and posterior thirds its upper surface 

 slopes downward and backward, and at the back its vertical diameter 

 is less than the transverse diameter. The orbitosphenoids cover the 

 sides of the presphenoid in the form of thin plates, which behind and 



