210 THE SKELETON. 



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 vessels. Farther back in the 

 middle line is the ethmoidal spine, bounded behind by an elevated ridge, sepa- 

 rating two longitudinal grooves which support the olfactory tracts. 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, 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 line, but becomes wider at the side of the skull. It is bounded in front by 

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

 and the ridge forming the anterior margin of the optic groove ; behind, by the 

 superior border of the petrous portion of the temporal and the dorsum ephippi ; 

 externally by the squamous portion of the temporal, anterior inferior angle of the 

 parietal bone, and greater wing of the sphenoid. It is traversed by four sutures, 

 the squamo-parietal, spheno-parietal, squamo-sphenoidal, and petro-sphenoidal. 



In the middle line, from before backward, is the optic groove, which supports 

 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 2^ocesses, to which 

 are attached processes of the tentorium cerebelli. Farther back 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, the dorsum ephippi, surmounted at each superior 

 angle by a tubercle, the posterior clinoid process ; beneath the latter process is a 

 notch, 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 process, and presents along its outer margin a ridge of 

 bone. 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 convolutions 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 large branches, an 

 anterior and a posterior ; the former passing upward and forward to the anterior 

 inferior angle of the parietal bone, the latter passing upward and backward. 

 The following foramina may also be seen from before backward : 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 sometimes completed externally by the orbital plate of the frontal 

 bone. It transmits the third, the fourth, the three branches of the ophthalmic 

 division of the fifth, the sixth nerve, some filaments from the cavernous plexus of 

 the sympathetic, the orbital branch of the middle meningeal artery, a recurrent 

 branch from the lachrymal artery to the dura mater, and the ophthalmic vein. 

 Behind the inner extremity of the sphenoidal fissure is the foramen rotundum, for 

 the passage of the second division of the fifth or superior maxillary nerve ; still 

 more posteriorly is seen a small orifice, the foramen Vesalii, an opening situated 

 between the foramen rotundum and ovale, a little internal to both : it varies in size 

 in different individuals, and is often absent ; when present, it transmits a small vein. 

 It opens below into the pterygoid fossa, just at the outer side of the scaphoid 

 depression. Behind and external to the latter opening is the foramen ovale, which 

 transmits the third division of the fifth or inferior maxillary nerve, the small 

 meningeal artery, and the small petrosal nerve. 1 On the outer side of the foramen 

 ovale is the foramen spinosum, for the passage of the middle meningeal artery ; and 



1 See footnote, p. 182. 



