178 THE SKELETON. 



an aperture formed by the frontal bone and the crista galli of the ethmoid, which, 

 if pervious, transmits a small vein from the nose to the superior longitudinal 

 sinus ; behind the foramen coecum, the crista galli, the posterior margin of which 

 affords attachment to the falx cerebri ; on either side of the crista galli, the 

 olfactory groove, which supports the bulb of the olfactory nerve, and is per- 

 forated by three rows of orifices for its filaments, and in front by a slit-like 

 opening, for the nasal branch of the ophthalmic 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, transmits the anterior ethmoidal artery and the nasal 

 nerve, which runs in a depression along the surface of the ethmoid, to the slit- 

 like opening above mentioned ; whilst the posterior ethmoidal foramen opens 

 at the back part of this margin under cover of the projecting lamina of the 

 sphenoid, and transmits the posterior ethmoidal artery and vein to the posterior 

 ethmoidal cells. Further back in the middle line is the ethmoidal spine, bounded 

 behind by an elevated ridge, separating a longitudinal groove on each side which 

 supports the olfactory nerve. The anterior fossa presents laterally eminences 

 and depressions for the convolutions of the brain, and grooves for the lodgment 

 of the anterior meningeal arteries. 



The Middle fossa, somewhat deeper than the preceding, is narrow in the 

 middle, and becomes wider as it expands laterally. It is bounded in front by 

 the posterior margin of the lesser wing of the sphenoid, the anterior clinoid 

 process, and the anterior margin of the optic groove ; behind, by the petrous 

 portion of the temporal, and basilar suture ; externally, by the squamous por- 

 tion of the temporal, and anterior inferior angle of the parietal bone, and is 

 separated from its fellow by the sella Turcica. It is traversed by four sutures, 

 the squamous, spheno-parietal, spheno-temporal, and petro-sphenoidal. 



In the middle line, from before backwards, is the optic groove, which sup- 

 ports the optic commissure, and terminates on each side in the optic foramen, 

 for the passage of the optic nerve and ophthalmic artery ; behind the optic 

 groove is the olivary process, and laterally the anterior clinoid processes, to 

 which are attached the folds of the dura mater, which form the cavernous 

 sinuses. Separating the middle fossas is the sella Turcica, a deep depression, 

 which lodges the pituitary gland, bounded in front by a small eminence on 

 either side, the middle clinoid process, and behind by a broad square plate of 

 bone, surmounted at each superior angle by a tubercle, the posterior clinoid 

 process ; beneath the latter process is a groove, for the sixth nerve. On each 

 side of the sella Turcica is the cavernous groove ; it is broad, shallow, and 

 curved somewhat like the italic letter /; it commences behind at the foramen 

 lacerum medium, and terminates on the inner side of the anterior clinoid pro- 

 cess. This groove lodges the cavernous sinus, the internal carotid artery, and 

 the nerves of the orbit. The sides of the middle fossa are of considerable 

 depth ; they present eminences and depressions for the middle lobes of the 

 brain, and grooves for the branches of the middle meningeal artery ; the latter 

 commence on the outer side of the foramen spinosum, and consist of two largo 

 branches, an anterior and a posterior; the former passing upwards and for- 

 wards to the anterior inferior angle of the parietal bone, the latter passing 

 upwards and backwards. The following foramina may also be seen from before 

 backwards. Most anteriorly is the foramen lacerum anterius, or sphenoidal 

 fissure, formed above by the lesser wing of the sphenoid ; below, by the greater 

 wing; internally, by the body of the sphenoid; and completed externally by 

 the orbital plate of the frontal bone. It transmits the third, fourth, the three 

 branches of the ophthalmic division of the fifth, the sixth nerve, and tho 

 ophthalmic vein. Behind the inner extremity of the sphenoidal fissure is tho 

 foramen rotundum, for the passage of the second division of the fifth or 

 superior maxillary nerve; still more posteriorly is seen a small orifice, tho 

 foramen Vesalii, an opening, situated between the foramen rotundum and ovale, 



