32 TEMPORAL BONE. 



of the meatus auditorius internus. Above the meatus auditorius in- 

 ternus is a small oblique fissure, and a minute foramen ; the former 

 lodges a process of the dura mater, and the foramen gives passage to a 

 small vein. Further outwards, towards the mastoid portion of the 

 bone, is a small slit, almost hidden by a thin plate of bone ; this is the 

 aquaeductus vestibuli, and transmits a small artery and vein of the ves- 

 tibule and a process of dura mater. Below the meatus, and partly 

 concealed by the margin of the posterior border of the bone, is the 

 aquceductus cochlea, through which passes a vein from the cochlea to 

 the internal jugular vein, and a process of dura mater. 



The meatus auditorius internus is about one-third of an inch in 

 depth, and pursues a slightly oblique course in relation to the petrous 

 portion of the temporal bone, but a course directly outwards in 

 relation to the cranium. At the bottom of the meatus, and upon its 

 anterior aspect, is a reniform fossa, the concave border of which 

 is directed towards the entrance of the meatus. The reniform fossa 

 is divided into an upper and lower compartment by a sharp ridge, 

 which is prolonged for some distance upon the anterior wall of the 

 meatus and sometimes as far as its aperture ; in either case it marks 

 the situation of the two nerves, facial and auditory, which constitute 

 the seventh pair, and enter the meatus. Along the convexity of the 

 reniform fossa, and arranged in a curved line from above downwards, 

 are four of five openings, the two upper ones being the largest, and 

 occupying the superior compartment of the reniform fossa, and the 

 two or three inferior ones, smaller than the upper, the inferior com- 

 partment. Behind the latter, at the distance of a line and a half, and 

 on the posterior wall of the meatus is a cluster of three or four oblique 

 openings, two of which are minute. The inferior and larger com- 

 partment of the reniform fossa presents a well-mailed spiral groove, 

 which commences on the convex border of the fossa, immediately below 

 the line of openings above described, and, sweeping round the con- 

 vexity of the inferior compartment, and becoming deeper as it proceeds, 

 terminates by a small round aperture in the centre of the spire. The 

 uppermost of the openings of the reniform fossa is the aperture of the 

 aquseductus Fallopii and gives passage to the facial nerve. The rest 

 are cul de sacs, pierced at the bottom by a number of minute foramina 

 for the passage of filaments of the vestibular nerve, while the cluster 

 of three openings on the posterior wall of the meatus are intended for 

 single filaments of the same nerve. The spiral groove corresponds 

 with the base of the cochlea, and being pierced by a number of 

 minute foramina for filaments of the cochlear nerve, is named tractus 

 spiralis foraminulentus. The opening in the centre of the spiral im- 

 pression leads into a canal which occupies the central axis of the 

 modiolus, and is thence called tubulus centralis modioli. 



The basilar surface is rough and irregular, and enters into the 

 formation of the under surface of the base of the skull. Projecting 

 downwards, near its middle, is a long sharp spine, the styloid process, 

 occasionally connected with the bone only by cartilage and lost during 



