394 NEUROLOGY, OR ANATOMY OF NERVOUS SYSTEM 



nates above in a bony process, the infundibulum, which blends 

 with the cupola or last half turn of the spiral canal. Here 

 the two scalse communicate by a small opening, the helicotrema. 

 Around the modiolus, along the attachment of the lamina 

 spiralis, is the spiral canal of the modiolus, containing a gan- 

 gliated portion of the cochlear nerve, the ganglion spirale. 



The spiral canal is If inches long and T V inch in diameter 

 at its widest part, which is below. The scala vestibuli com- 

 municates with the vestibule by the foramen above mentioned, 

 and a part of it, marked off by a membrane, is called the scala 

 media (see below). The scala tympani commences at the 

 fenestra rotunda, and close to its commencement is the opening 

 of the aquceductus cochleae, by which it communicates with the 

 subarachnoid space, and in which there is transmitted a small 

 vein to the internal jugular. The spiral lamina ends above 

 in a hook-like process, the hamulus, which partly bounds the 

 helicotrema. 



The membranous labyrinth is contained within the osseous 

 labyrinth, having a similar form, though smaller and separated 

 from it by the perilymph. It contains the endolymph and 

 receives the distribution of the auditory nerve. In the vestibule 

 it consists of the utricle and the saccule. 



The utricle is in the upper and back part, its cavity com- 

 municating by five apertures with the membranous semicircular 

 canals. It is in contact with the fovea hernielliptica. 



The saccule is in the fovea hemispherica, and communicates 

 with the utricle by means of a small tube which passes into 

 the aquseductus vestibuli, and there joins a canal (saccus endo- 

 lymphaticus), which canal is prolonged from the utricle and 

 ends in a blind extremity; and with the scala media by means of 

 the canalis reuniens. 



The membranous semicircular canals are similar in shape 

 to but are only from one-fifth to one-third the diameter of 

 the bony canals; the ampullae, however, are relatively large. 

 Two small masses of calcium carbonate are found in the utricle 

 and saccule. They are called the otoliths. 



In the cochlea the membranous labyrinth is represented 

 by the scala media and the parts therein, which , are formed 

 as follows: 



Along the edge of the spiral lamina the periosteum on its 

 upper surface is raised up like a C to form the limbus laminoe 



