116 THE SKELETON 



The Middle Cranial Fossa, situated on a lower level than the anterior, 

 consists of a central and two lateral portions. In front it is limited by the posterior 

 borders of the lesser wings of the sphenoid and the anterior margin of the optic 

 groove, behind by the dorsum sellse and the upper angle of the petrous portion 

 of both temporal bones. Laterally it is bounded on each side by the squamous 

 portion of the temporal, the great wing of the sphenoid, and the parietal bone, 

 whilst the floor is formed by the body and great wings of the sphenoid and the 

 anterior surface of the petrous portion of the temporals. It contains the follow- 

 ing sutures: — spheno-parietal, petro-sphenoidal, squamo-sphenoidal, squamous, 

 and a part of the transverse suture. The central portion of the fossa presents 

 from before backward: 



The optic groove, above and behind which is the optic chiasma. 



The optic foramen on each side, transmitting the optic nerve and ophthalmic artery. 



The tuberculum sellae, indicating the line of junction of pre- and post-sphenoid elements. 



The anterior clinoid processes. 



The fossa hypophyseos or sella turcica, with the middle clinoid processes, and grooves for 

 the internal carotid arteries. The dorsum sellae, with the posterior clinoid processes, and 

 notches for the sixth pair of cranial nerves. 



The central portion is in direct relation with the parts of the brain within the circle of 

 Willis. 



The lateral portions are of considerable depth and marked by numerous elevations and 

 depressions corresponding to the convolutions of the temporal lobes of the brain, and by grooves 

 for the branches of the middle and small meningeal vessels. The following foramina are seen 

 on each side: — 



The superior orbital (sphenoidal) fissure, leading into the orbit and transmitting the third, 

 fourth, three branches of the ophthalmic division of the fifth and sixth cranial nerves, some 

 filaments from the cavernous plexus of the sympathetic, an ophthalmic vein, the orbital branch 

 of the middle meningeal, and a recurrent branch of the lacrimal artery. 



The foramen rotundum, for the passage of the second division of the fifth nerve into the 

 pterygo-palatine fossa. 



The foramen ovale, which transmits the third division of the fifth nerve with its motor 

 root (mandibular nerve), the small meningeal artery, and the small superficial petrosal nerve. 



The foramen Vesalii (not always present) for a small vein. 



The foramen spinosum, for the middle meningeal artery and its vense comitantes; also the 

 N. spinosus. 



The foramen lacerum is the irregular aperture between the body and great wing of the 

 sphenoid, and the apex of the petrous portion of the temporal. In the recent state it is closed 

 below by a layer of fibro-cartilage which is perforated by the Vidian nerve, a meningeal branch 

 of the ascending pharyngeal artery, and an emissary vein. The carotid canal opens on its 

 lateral wall and the pterygoid (Vidian) canal in front. 



On the anterior surface of the petrous portion of the temporal bone are seen: — 



A depression which lodges the semilunar (Gasserian) ganglion. 



The hiatus canalis facialis for the great superficial petrosal nerve and the petrosal branch 

 of the middle meningeal artery. 



The accessory hiatus for the small superficial petrosal nerve. 



A minute foramen for the external superficial petrosal nerve. 



The eminentia arcuata, formed by the superior semicircular canal. 



Anterior and slightly lateral to the eminentia arcuata the bone is exceedingly thin and 

 translucent, forming the roof of the tympanum (tegmen tympani). When the dura mater is 

 in situ, the depression lodging the semilunar ganglion is converted into a foramen, traversed by 

 the fifth nerve, and in the same way the notch on the side of the dorsum selljB is converted into 

 a foramen for the sixth nerve. In many skulls the middle clinoid process is prolonged toward 

 the anterior clinoid process, with which it may be joined to complete a foramen for the internal 

 carotid artery. The grooves for the middle meningeal vessels are sometimes converted into 

 canals or tunnels for a short distance, especially in old skulls. The bones most deeply marked 

 are the squamous portion of temporal, the great wing of the sphenoid, and the parietal. 



The PosTEuioii Cranial Fossa is the deepest and largest of the series. It is 

 bounded in front by the dorsum sella of the sphenoid and on each side by the 

 superior border of the petrosal, and the mastoid portion of the temporal bone, the 

 po.stcrior inferior angle of the parietal, and the groove on the occipital bone for 

 the transverse sinus; each of the bones mentioned takes part in the formation of 

 its floor. 



In the recent state the fossa lodges the cerebellum, pons, and medulla, and is 

 roofed in by the tentorium ccrebclli, a tent-like process of the dura mater attached 

 to tlie ridges limiting the fossa above. It communic^ates witii the general cranial 

 cavity by means of the foramen ovale of Pacchionius, a large opening bounded 

 in front by the clivus (basilar groove) and behind by the anterior free edge of the 

 tentorium. 



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