36 



THE SKELETON 



Tlie posterior surface is l)ounded above by the superior border, Avhicb serves 

 for the attaehnient oi the tentorium cerebelh, and is grooved lor the su})erior petrosal 

 sinus; near the apex, this border presents the trigeminal notch (eonverted into 

 a foramen by the tentorium) for the transmission of the trigeminal nerve. This 

 border in old skulls sometimes terminates in a spiculum of bone — the petro-sphe- 

 noidal process — and extends to the dorsum ephippii, and eompletes a foramen 

 (petro-sphenoidal) whieh transmits the sixth nerve. Near the middle of the 

 posterior surfaec is an oblique inlet, the internal auditory meatus, which receives 



Fig, 44.— The Left Temporal Bone. (luner view.) 



FOR MIDDLE MENINGEAL ARTERY f" 



LATERAL SINUS 



THE GROOVE FOR SUPERIOR 



PETROSAL SINUS feg;, '■ g— 

 MASTOID FORAMEN — ^^, V 

 AQUEOUCTUS VESTIBULI ^ — ^ 



AQUEDUCTUS COCHLE/f 





PETROSAL 



REMNANT OF FLOCCULAR FOSSA 

 INTERNAL AUDITORY MEATUS 



FOR OCCIPITAL 



the auditory and facial nerves and the auditory artery. The meatus is altout 10 

 mm. deep, and to be properly examined the surface of the bone should be cut 

 away, or the parts studied in the petrosal of a foetus at or near the ninth month, 

 for it is at this date relatively large and shallow. 



The fundus of the meatus is divided by a transverse ridge of bone, the f ale if or yn crest, into a 

 superior and inferior fossa. Of these, the superior is the smaller, and presents anteriorly the 

 beginning of the aqueduct of Fallopius ; this transmits the seventh nerve. The rest of the sur- 

 face above the crest is dotted with small foramina (the superior cribriform area) which transmit 

 nerve-twigs to the fovea hemielliptica and the ampullae of the superior and external semicircular 

 canals. Below the crest there are two depressions and an opening. Of these, an anterior cuiled 



Fig. 45.— The Foramina in the Fundus of the Left Internal Auditory Meatus of a 

 Child at Birth (y). (Diagrammatic.) 



SUPERIOR FOSSA 



SUPERIOR CRIBRIFORM AREA 



MIDDLE CRIBRIFORM AREA 

 FORAMEN SINGULARE 



ENTRANCE TO THE AQUEDUCT OF FALLOPIUS 



FALCIFORM CREST 



'^ S^rff^ ORIFIC 



•aitr. 



SPIRAL CRIBRIFORM TRACT 



■|CE OF THE CANAL OF THE MODIOLUS 



tract (the spiral crihrifurm tract) with a central foramen (foramen centrale codilearc) marks 

 the base of the (•(tchlea ; the central foramen indicates the orifice of the, canal of the modio- 

 lus, and the smaller foramina transmit the cochlear twigs of the auditory nerve. The pos- 

 terior opening (loranien singulare) is fur the nerve to the ami)ulla of the jiosterior semicircular 

 canal. The middle depression (middle cribriform area) is dotted with minute foramina for the 

 nerve-twigs to the saccule, which is lodged in the fovea hemisjiherica. The inferior fossa is sub- 

 divided l»y a low vertical crest. The fossa in front of the crest is the fosfntla cochlenris, and the 

 recess behind it is the fossitla vcstihiilaris. 



Behind the meatus is a small slit (aqueductus vestibuli) which lodges the 

 ductus endolymphaticus; in the adult it is occupied by a small arteriole and venule 



