I5I2 



HUMAN ANATOMY. 



part of the spherical recess, the crista vestibuli divides into two limbs between which 

 is the recessus cochlearis, which lodges the beginning of the ductus cochlearis and 

 is pierced by a number of small openings for the passage of nerve filaments to this 

 duct. The numerous minute holes piercing the crista (pyramid) and the elliptical 



recess collectively form 

 Fig 1266. the macula cribrosa 



superior (Fig. 1266) and 

 transmit branches of the 

 vestibular nerve to the 

 utricle and to the ampullae 

 of the superior and hori- 

 zontal semicircular canals. 

 Below and behind the re- 

 cessus ellipticus lies a 



Crus coinmun 



Aqjiaeductiis 

 vestibuli 



Recessus 



ellipticus 



Macula inferior 



Crista vestibuli 



Recessus sphseri- 



cus with macula 



media 



Superior 



semicircular 



canal 



•Ampulla 



] Macula crib- 

 / rosa superior 



Facial canal 



Oval %vindow 



Lamina spiralis 



Section of right bony labyrinth passing through plane of superior semi- 

 circular canal ; anterior wail of vestibule is seen from behind. X 4- 



groo\'e, the fossula sul- 

 ciformis, which deepens 

 posteriorly into a very 

 small canal, the aqueduct 

 of the vestibule (aquae- 

 ductus vestibuli) which runs 

 in a slightly curved course 

 to the posterior surface of 

 the petrous portion ,of the 

 temporal bone, where it 

 ends in a slit-like opening, 

 the apertura externa aquaeductus vestibuli, situated between the internal 

 opening of the internal auditory canal and the groove for the lateral sinus. The 

 canal transmits the ductus endolymphaticus and a small vein. The anterior wall of 

 the vestibule is pierced by the large opening leading into the scala vestibuli of the 

 cochlea. Near this aperture is seen the beginning of the lamina spiralis ossea which 

 lies on the floor of the vestibule below the oval window. Posteriorly the vestibule 

 directly communicates with the semicircular canals by five round openings. 



The Semicircular Canals. — The three bony semicircular canals — the superior, 

 the posterior and the horizontal — lie behind the vestibule and are perpendicular to 

 one another (Fig. 1265). Their disposition is such that the planes of the three canals 

 correspond with the 

 sides of the corner of a 

 cube, suggestively re- 

 calling the relations of 

 the three cardinal 

 planes of the body — 

 the sagittal, frontal and 

 transverse. Each canal 

 possesses at one end a 

 dilatation, called the 

 osseus ampulla. The 

 superior canal (ca- 

 nalis superior J lies farth- 

 est front and in a nearly 

 vertical plane at right 

 angles to the long axis 

 of the petrous portion 

 of the temporal bone, 

 whilst the plane of the 

 longest canal, the pos- 



Ampulla of 

 superior' cana' 



Ampulla of 

 horizontal cana' 



Facial canal 



Oval (vestibular) 

 window 



Lamina spiralis 



Small end of 

 posterior canal 



Crus commune 



Small end of 

 horizontal canal 



Ampulla of 

 posterior canal 



Recessus 

 cochlearis 



Round (cochlear) window- 



Section of right bony labyrinth passing through plane of superior semicircular 

 canal ; posterior wall of vestibule is seen from before. X ^• 



terior (canalis posterior) is appro.ximately parallel to it. The external portion of 

 the horizontal semicircular canal forms a prominence on the inner wall of the middle 

 ear above the facial canal, while the upper part of the superior semicircular canal 

 produces the conspicuous elevation, the eminentia arcuata, seen on the superior 



