CHAP. XVIII.] THE COCHLEA. 75 



the jugular fossa, and supposed to transmit a small vein. The 

 spiral canal describes about two turns and a half, of which the first, 

 passing round the large base of the modiolus, takes much the widest 

 sweep, so as to encircle most of the second turn. The inner wall of 

 this coiled canal, as has been shown by Ilg, forms the outer wall of 

 the modiolus. 



The spiral canal of the cochlea is subdivided into two passages by 

 an osseo-membranous lamina, extended between its modiolar and 

 peripheral wall, and of course taking the same spiral direction as the 

 canal itself. This is the lamina spiralis, the fundamental element 

 of the cochlea, on which the nervous tubules are spread out. More 

 than half its breadth on the side of the modiolus is formed by a very 

 brittle osseous process from the modiolus, called the osseous zone, 

 enclosing minute channels continuous with those of that part, and 

 transmitting the nerves; its opposite or outer portion is membranous 

 and muscular, and connects the outer thin edge of the osseous zone 

 to the outer wall. The osseous zone commences gradually within 

 the vestibule, and enters the spiral canal between the vestibular and 

 tympanic openings of the cochlea, forming, with the help of the 

 membranous extension, a complete septum between them. The 

 passages, or scalce, into which the spiral lamina divides the canal, 

 correspond, therefore, respectively to those chambers ; the upper, 

 towards the apex of the cochlea, scala vestibuli, the lower, towards 

 its base, scala tympani. These scales are, on the whole, pretty 

 equal in size; the vestibular scala is, however, the smaller at the base, 

 the tympanic, near the apex, of the coil ; and the latter ceases ere 

 it reaches the summit. At the apex of the cochlea the parts have 

 an arrangement difficult to describe, though easily understood when 

 seen. The axis, 110 longer hollow, and containing nerves, is reduced 

 to a delicate lamella at about half a turn from the dome-like summit, 

 or cupola, formed by the last part of the spiral canal. This lamella, 

 which is the real apex of the modiolus, immediately expands, stretches 

 upwards, and becomes more twisted on itself, so as to include part, or 

 all of the last half turn of the cochlear canal, being termed from its 

 appearance as viewed from below, the infundibulum, or funnel. The 

 wide part of this imperfect funnel is directed towards the cupola, 

 with which it blends. It is not open above, but on the side, and 

 it is, in fact, the outside of the last half turn of the canal, projecting 

 into the turn below. 



The osseous zone of the spiral lamina ceases with the hoJlow 

 modiolus at the slender lamella already mentioned, terminating by 

 a small projecting hook (hamulus), the concave border of which is 



