578 ANATOMY IN A NUTSHELL. 



perforated by numerous foramina for branches of the auditory nerve. It is 

 directed toward the meatus auditorius interims. 



3. The spiral canal (canalis spiralis modioli) is the space between the 

 modiolus and the outer wall of the cochlea. It diminishes in diameter as it 

 approaches the apex of the cochlea and ends in a closed extremity (cupola) 

 after making two and three-fourths turns. 



4. The lamina spiralis is a thin osseous plate projecting into the spiral 

 canal from the modiolus reaching half way across the spiral canal. It winds 

 around the modiolus and ends near the apex in a hook-like process (the ham- 

 ulus). Helicotrema is the deficiency in the last half turn of the cochlea. The 

 membrana basilaris and the membrana Reissner are two membranes which 

 extend from the free border of the lamina spiralis and are connected with the 

 outer wall of the cochlea. Between them is the scala media (cochlear duct). 

 The scala media divides the spiral canal into three parts, the scala tympani 

 below and the scala vestibuli above, and between these two the scala media. 

 The scala tympani opens into the tympanum at the fenestra rotunda, however, 

 this opening is closed by the membrana secundaria. The scala vestibuli opens 

 into the vestibule. Where these two scalse communicate with each other at 

 the summit of the cochlea is called the helicotrema. 



The membranous labyrinth is situated within the bony labyrinth from 

 which ii is separated by the perilymph. 



The utricle lies partly in the fovea hemielliptica and is a flattened, oblong 

 sac. h is filled with endolymph and communicates with the saccule through 

 a small tube in the aqueductus vestibuli. The membranous semicircular canals 

 open into the utricle by five orifices. 



1. Macula acustica utricularis is a thickened portion of the walls of the 

 utricle which contain calcareous masses (otoliths) in which are distributed 

 filaments of the vestibular branch of the auditory nerve. 



2. DUCTUS ENDOLYMPHATICUS which has been previously described. 



The saccule, which is smaller than the utricle, receives branches of the 

 auditory nerve through the openings in the fovea hemispheriea, and these 

 branches end in the thicked part of the wall which is covered with otoliths. 



The membranous semicircular canals are the same shape as the osseous 

 semicircular canals and are about one-fourth the diameter of the osseous canals. 

 Their enlarged extremities are called ampulla. 



The membranous cochlea (cochlear duct) (scala media) is a spiral tube 

 enclosed in the spiral canal of the osseous cochlea between the scala vestibuli 

 and the scala tympani. It is filled with endolymph and contains the organ 

 ol Cortl which is a complex arrangement of modified epithelial cells including 

 the rods of Corti and the auditory cells. 



Blood Supply.— From the auditory artery which enters the internal 

 auditory meati - and divides into branches for the cochlea and vestibule. The 

 veins empty into the internal jugular and into the superior petrosal sinus. 



Nerve Supply.- The auditory ne ve which is the nerve of special sense of 

 hearing. 



