100 OSTEOLOGY. 



The Internal or Cerebral Surface (fig. 62) presents three fossa} on each side, 

 called the anterior, middle and posterior fossae of the cranium. 



The Anterior Fossa is formed by the orbital plate of the frontal, the cribriform 

 plate of the ethmoid, the ethmoidal process and lesser wing of the sphenoid. It 

 is the most elevated of the three fossoe, convex externally where it corresponds to 

 the roof of the orbit, concave in the median line in the situation of the cribriform 

 plate of the ethmoid. It is traversed by three sutures, the ethmoido -frontal, 

 ethmo-sphenoidal, and fronto-sphenoidal ; and lodges the anterior lobe of the cere- 

 brum. It presents, in the median line, from before backwards, the commencement 

 of the groove for the superior longitudinal sinus, and crest for the attachment of 

 the falx cerebri; the foramen caecum, this aperture being formed by the frontal and 

 crista galli of the ethmoid, and, if pervious, transmitting a small vein from the nose 

 to the superior longitudinal sinus. Behind the foramen cascum is the crista galli, 

 the posterior margin of which affords attachment to the falx cerebri. On either 

 side of the crista galli is the olfactory groove, which supports the bulb of the 

 olfactory nerve, perforated by three rows of orifices which give passage to its 

 filaments; and in front by a slit-like opening, which transmits 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 its outer margin, transmits the nasal nerve, which 

 runs in a groove along its surface to the slit-like opening above mentioned ; whilst 

 the latter, the posterior ethmoidal foramen, opens at the back part of the margin 

 under cover of a projecting lamina of the sphenoid; it 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, sepa- 

 rating a longitudinal groove on each side which supports the olfactory nerve. 

 The anterior fossa presents laterally eminences and depressions for the convolu- 

 tions 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 tem- 

 poral, and basilar suture; externally, by the squamous portion 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 supports 

 the optic commissure, terminating 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, which afford 

 attachment to the folds of the dura mater, which form the cavernous sinuses. 

 Separating the middle fossa? 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 lodgment of 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 process. This groove lodges 

 the cavernous sinus, the internal carotid artery, and the orbital nerves. The sides 

 of the middle fossa are of considerable depth ; they present eminences and depres- 

 sions for the middle lobes of the brain, and grooves for lodging the branches of 

 .the middle meningeal artery ; the latter commence on the outer side of the fora- 

 men spinosum, and consist of two large branches, an anterior and a posterior ; the 

 former passing upwards and forwards 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 



