THE ENTIBE SKULL 



519 



FIG. 412. 



rior fossae. The anterior fossa is sharply limited behind by the 

 rounded posterior border of the small wings of the sphenoid ; the 

 middle fossa is limited behind by the superior border of the petrous 

 portions of the temporal. The student should now identify the fora- 

 mina and sutures seen on the external 

 aspects of the skull and the relations 

 between the outer and inner surfaces of 

 the cranial bones. (Fig. 412.) 



On the floor of the cavity in front, at 

 the lower end of the median crest on the 

 frontal bone, in the fronto-ethmoidal suture, 

 is the small foramen caecum, which in 

 some specimens transmits a vein from the 

 nose to the superior longitudinal sinus. 

 Behind the foramen is the triangular eth- 

 moidal crista galli for the attachment of 

 the falx cerebri ; on each side of this pro- 

 cess is the perforated part of the cribri- 

 form plate, forming a shallow olfactory 

 groove for the olfactory bulb of the brain. 

 At the posterior end of each lateral fronto- 

 suture is the posterior eth- 

 foramen for the posterior eth- 

 vessels ; further forward is the 

 anterior ethmoidal foramen, which trans- 

 mits the anterior ethmoidal vessels, and 

 also permits the nasal branch of the 

 ophthalmic division of the fifth cranial 

 nerve to pass from the orbit to the cranial 

 cavity. The nerve then lies in a groove 

 which leads from the foramen to a slit 

 at the anterior end of the suture, through 

 which it passes into the nasal cavity. 



On each side of the olfactory groove 

 the floor of the anterior cerebral fossa, formed by the orbital plate 

 of the frontal bone, is marked by ridges, outlining grooves for the 

 cerebral convolutions. Behind the cribriform plate are the ethmoidal 

 spine and the level anterior part of the upper surface of the anterior 



INTERNAL VIEW OF THE BASE OF 

 THE CRANIUM. THE LEFT SIDE. 



a, b, c, anterior, middle, and posterior 

 cranial tbssaj; 1, orbital plate of the 

 frontal bone; 2, small wing of the sphe- 

 noid bone; 3, great wing of the same; 



4, squamous portion of the temporal bone; 



5, petrous portion of the same ; G, mastoid 

 portion; 7, parietal bone; 8, occipital bone; 



9, olfactory fossa and ethmoidal crest; 



10, sella; 11, anterior clinoid process; 

 12, clivus; 13, occipital foramen; 14, 

 optic foramen; 15, foramen rotundum; 

 16, foramen ovale; 17, foramen spinosum 

 and groove from it, indicating the course 

 of the great meningeal vessels; 18, middle 

 lacerated foramen; 19, internal auditory 

 meatus; 20, jugular foramen; 21, condyloid 

 foramen ; 22, commencement of the groove 

 for the lateral sinus. The course of the 

 groove is observed along the horizontal 

 limb of the occipital cross, the postero- 

 inferior angle of the parietal bone, the 

 mastoid portion of the temporal, and the 

 jugular process of the occipital, termi- 

 nating at the jugular foramen. 



