192 



OSTEOLOGY 





by the lingula. This groove lodges the cavernous sinus and the internal carotid 

 artery, the latter being surrounded by a plexus of sympathetic nerves. 



The lateral parts of the middle fossa are of considerable depth, and support 

 the temporal lobes of the brain. They are marked by depressions for the brain 

 convolutions and traversed by furrows for the anterior and posterior branches 

 of the middle meningeal vessels. These furrows begin near the foramen spinosum, 

 and the anterior runs forward and upward to the sphenoidal angle of the parietal, 

 where it is sometimes converted into a bony canal; the posterior runs lateralward 

 and backward across the temporal squama and passes on to the parietal near 

 the middle of its lower border. The following apertures are also to be seen. In 

 front is the superior orbital fissure, bounded above by the small wing, below, by the 

 great wing, and medially, by the body of the sphenoid; it is usually completed 

 laterally by the orbital plate of the frontal bone. It transmits to the orbital 

 cavity the oculomotor, the trochlear, the ophthalmic division of the trigeminal, 

 and the abducent nerves, some filaments from the cavernous plexus of the 

 sympathetic, and the orbital branch of the middle meningeal artery; and from the 

 orbital cavity a recurrent branch from the lacrimal artery to the dura mater, and 

 the ophthalmic veins. Behind the medial end of the superior orbital fissure is 

 the foramen rotundum, for the passage of the maxillary nerve. Behind and lateral 

 to the foramen rotundum is the foramen ovale, which transmits the mandibular 

 nerve, the accessory meningeal artery, and the lesser superficial petrosal nerve. 1 

 Medial to the foramen ovale is the foramen Vesalii, which varies in size in different 

 individuals, and is often absent; when present, it opens below at the lateral side 

 of the scaphoid fossa, and transmits a small vein. Lateral to the foramen ovale 

 is the foramen spinosum, for the passage of the middle meningeal vessels, and a 

 recurrent branch from the mandibular nerve. Medial to the foramen ovale is 

 the foramen lacerum; in the fresh state the lower part of this aperture is filled up 

 by a layer of fibrocartilage, while its upper and inner parts transmit the internal 

 carotid artery surrounded by a plexus of sympathetic nerves. The nerve of the 

 pterygoid canal and a meningeal branch from the ascending pharyngeal artery 

 pierce the layer of fibrocartilage. On the anterior surface of the petrous portion 

 of the temporal bone are seen the eminence caused by the projection of the superior 

 semicircular canal ; in front of and a little lateral to this a depression corresponding 

 to the roof of the tympanic cavity; the groove leading to the hiatus of the facial 

 canal, for the transmission of the greater superficial petrosal nerve and the petrosal 

 branch of the middle meningeal artery ; beneath it, the smaller groove, for the pas- 

 sage of the lesser superficial petrosal nerve; and, near the apex of the bone, the 

 depression for the semilunar ganglion and the orifice of the carotid canal. 



The Posterior Fossa (fossa cranii posterior). -The posterior fossa is the largest 

 and deepest of the three. It is formed by the dorsum sellse and clivus of the 

 sphenoid, the occipital, the petrous and mastoid portions of the temporals, and the 

 mastoid angles of the parietal bones; it is crossed by the occipitomastoid and the 

 parietomastoid sutures, and lodges the cerebellum, pons, and medulla oblongata. 

 It is separated from the middle fossa in and near the median line by the dorsum 

 sellse of the sphenoid and on either side by the superior angle of the petrous por- 

 tion of the temporal bone. This angle gives attachment to the tentorum cerebelli, 

 is grooved for the superior petrosal sinus, and presents at its medial end a notch 

 upon which the trigeminal nerve rests. The fossa is limited behind by the grooves 

 for the transverse sinuses. In its center is the foramen magnum, on either side of 

 which is a rough tubercle for the attachment of the alar ligaments; a little above 

 this tubercle is the canal, which transmits the hypoglossal nerve and a meningeal 

 branch from the ascending pharyngeal artery. In front of the foramen magnum 



See footnote, page 150. 



