70 



THE SKULL AS A WHOLE. 



of the cribriform plate, usually between that and the frontal bone, and is connected by a groove 

 with the inner opening of the anterior internal orbital canal : the nerve is accompanied by the 

 nasal division of the anterior ethmoidal artery. 



The middle fossa, on a lower level than the anterior, consists of a median and 

 two lateral parts. The median part is small, being formed by the olivary eminence 

 and sella turcica of the sphenoid bone, and limited behind by the dorsum sells. The 

 lateral part on each side, formed by the great wing of the sphenoid, the squamous 

 part, and the anterior surface of the petrous part of the temporal, lodges the temporal 

 lobe of the cerebrum. The foramina of the middle fossa are the optic foramen, 

 sphenoidal fissure, foramen rotundum, foramen ovale, foramen spiuosum, foramen 

 lacerum and hiatus Fallopii. 



Fig. 72. INTERNAL BASE OF THE 

 SKULL, (Allen Thomson.) J 



1, anterior fossa and roof of the 

 orbit, as formed by the frontal bone ; 

 between 2 and 3, the foramen caecum, 

 crista galli and cribriform plate of 

 ethmoid ; 3, ethmoidal spine of the 

 sphenoid ; 4, lesser wing of sphenoid 

 terminating posteriorly in the anterior 

 clinoid process, inside which is the 

 optic foramen ; 5, placed in the pitui- 

 tary fossa, behind the olivary emin- 

 ence and transverse groove of the 

 optic commissure ; 6, dorsum sellse, 

 terminating in the posterior clinoid 

 processes ; 7, foramen rotundum, in 

 front of which, but not seen in the 

 figure, is the sphenoidal fissure ; 8, 

 foramen ovale ; 9, foramen spiuosum ; 



10, on the petrous bone, near its apex, 

 and to the inside of the hollow occu- 

 pied by the Gasserian ganglion ; in 

 front of this is the foramen lacerum ; 



11, in front of the eminence of the 

 superior semicircular canal, and be- 

 hind the hiatus Fallopii ; 12, upper 

 border of the petrous, marked by the 

 superior petrosal groove ; 13, the 

 posterior surface of the petrous to 

 the inside, the internal auditory 

 meatus, behind, the scale of bone 

 covering the aqueduct of the vestibule ; 

 14, basilar groove ; 15, anterior con- 



dylar foramen ; 16, jugular foramen ; 17, groove of the lateral sinus ; 18, internal occipital protube- 

 rance, and running\lown from it the internal occipital crest ; between 17 and 18, the upper part of the 

 groove of the lateral sinus, between 17 and 16, the lower part ; 19, cerebellar fossa. 



Through the optic foramen the optic nerve and the ophthalmic artery enter the orbit. The 

 sphenoidal fissure (foramen lacerum anterius) also opens into the orbit ; it gives passage to 

 the third, fourth, ophthalmic division of the fifth, and the sixth nerves, and the ophthalmic 

 veins. By the foramen rotundum the superior maxillary nerve passes into the spheno-max- 

 illary fossa. The foramen ovale and foramen spinosum lead into the zygomatic fossa : the 

 former transmits the inferior maxillary nerve, the small meningeal artery, and two or three 

 emissary veins ; the latter, the large meningeal vessels. 



The foramen lacerum (medium) is an irregular aperture between the apex of the petrous 

 and the body and great wing of the sphenoid, and in the recent state is closed below by a mass 

 of fibrous tissue ; the carotid canal opens on its external wall, the Vidian canal anteriorly. 

 The lingula projecting backwards from the body of the sphenoid effects a partial, sometimes 

 a complete subdivision of the space : by the inner part the carotid artery enters the cranial 

 cavity ; and through the external, the large superficial petrosal nerve, coming from the hiatus 

 Fallopii, reaches the posterior orifice of the Vidian canal. 



The posterior fossa, deeper and larger than the others, extends back to 

 the occipital protuberance, and lodges the cerebellum, medulla oblongata and pons. 



