THE SKULL AS A WHOLE 



125 



posterior margin of which affords attachment to the falx cerebri ; on either side of 

 the crista galli, the cribriform plate, which supports the olfactory bulb, and presents 

 three rows of foramina for the transmission of its nerve filaments, and in front a 

 slit-like opening (nasal slit) for the nasal branch of the ophthalmic division of the 

 trigeminal nerve. On the outer side of each olfactory groove are the internal 

 openings of the anterior and posterior ethmoidal foramina, the former situated about 

 the middle of the outer margin of the olfactory groove. The anterior ethmoidal 

 foramen transmits the anterior ethmoidal vessels and the nasal nerve, which latter 

 runs in a depression along the surface of the ethmoid to the slit-like opening 

 above mentioned; while the posterior ethmoidal foramen opens at the back part 

 of this margin under cover of the projecting lamina of the sphenoid, and trans- 

 mits the posterior ethmoidal vessels. Farther back in the middle line is the eth- 

 moidal spine, bounded behind by a slight elevation, separating two shallow longi- 



FIG. 95. Base of the skull. Interior view. 



tudinal grooves which support the olfactory lobes. Behind this is a transverse 

 sharp ridge, running outward on either side to the anterior margin of the optic 

 foramen, and separating the anterior from the middle fossa of the base of the skull. 

 The anterior fossa presents, laterally, depressions for the convolutions of the cere- 

 brum and grooves for the lodgement of the anterior meningeal arteries. 



The middle fossa (fossa cranii media) (Fig. 94), deeper than the preceding, is 

 narrow in the middle line, but becomes wider at the side of the skull. It is bounded 

 in front by the posterior margin of the lesser wings of the sphenoid, the anterior 

 clinoid processes, and the ridge forming the anterior margin of the optic groove; 

 behind, by the superior border of the petrous portions of the temporal and the dor- 

 sum sella-; externally, by the squamous portions of the temporal and the anterior 

 inferior angle of the parietal bones and greater wings of the sphenoid. On each 

 side it is traversed by four sutures, the squamoparietal, sphenoparietal, squarno- 



