ORGANS OF THE BODY. 657 



The arrangement of nervous elements in the sacculus rotundus varies in 

 some points, though in the main the same. 



In approaching the macula, the low cylindrical elements covering the 

 walls of the saccule are observed to give place to long, columnar, distinctly 

 nucleated cells, with yellowish contents, above whose free border filaments 

 are seen to project. 



Minute examination reveals that of these very decomposable elements 

 there are at least two forms, probably corresponding to the cylinder and 

 fibre cells of Schultze. These were also seen and sketched by Koelliker 

 in the saccus hemiellipticus of the ox years ago. One species present 

 long, narrow fusiform bodies without nuclei, but bearing on their ends those 

 filaments 0'0221-0'0226 mm. long, which, as we have already seen, pro- 

 ject beyond the surface of the nerve epithelium. These auditory filaments 

 were discovered long ago by Schultze in mammals, and from Odenius we 

 learn that they are also to be found in the septum nerveum of the human 

 ampullae. 



The connection of these filamentous bodies with the axis cylinders, 

 which certainly penetrate into the epithelium, requires, however, further 

 proof in our opinion. 



325. 



Let us turn now finally to the consideration of the cochlea (fig. 606). 



This spiral canal, which performs in the human ear two and a half 

 turns, is divided into two passages, which have long been known as the 

 scalce, the upper, named scala vestibuli (V), and the lower, scala tympani 

 (T), by a spiral plate, the lamina spiralis (q-i). Besides these, it pre- 

 sents also a third and more important intermediate space, the canalis coch- 

 learis of Reissner (Cf). 



The lamina spiralis (from q to i) consists of an internal bony and an 

 external soft or membranous portion. The first of these, an outgrowth from 

 the modiolus or central pillar, is about half the breadth of the whole leaf. 

 It is not, however, alike in all the turns, being broadest in the first, and 

 becoming gradually narrow as it ascends, until it finally terminates in the 

 last half in a hook, hamulus. 



This osseous spiral plate, lamina spiralis ossea, presents two lamellae of 

 compact bony tissue the upper facing the scala vestibuli, the lower the 

 scala tympani, and between these, porous tissue, through which run the 

 freely intercommunicating passages for the transmission of vessels and 

 nerves. Near the junction with the membranous portion these passages 

 unite to form a single fissure, bounded by the two osseous lamellae, both of 

 which terminate together here likewise. 



The membranous portion is directly and horizontally prolonged outward 

 from the bony partition. It is known as the lamina spiralis membranacea, 

 or memlrana bas-ilaris. It presents about the same breadth throughout 

 (O45 mm.), and is attached to the inner surface of the outer wall of the 

 cochlea. 



But as we first learned from Reissner and Koelliker, there springs 

 further, within the scala vestibuli, and near the line of junction of the 

 lamina ossea with the membranacea (), another membrane (R), which 

 ascending obliquely upwards and outwards reaches the inner surface of 

 the external wall of the cochlea, where it is attached. This is known 

 as the membrane of Reissner. 



Thus, a narrow passage is cut off from the scala vestibuli, lying external 



