LAMINA SPIRALIS AND SCALA OF THE COCHLEA. 467 



This last portion of the central pillar is called the Infundilu- 

 lum. It is hollow ; and the portion of bone which covers its 

 cavity, constitutes the basis of the inverted cone and the apex 

 of the cochlea. It is called the Cupola. 



The tube thus wound round the modiolus, or the cochlea, is 

 divided from the beginning to the end by a partition. 



The cavities are called Scala, and the partition Lamina 

 Spiralis. 



The Lamina Spiralis is made up of four parallel strips, 

 which compose its breadth. 



1st. A plate of bone. 



2d. Outside of this, a softer plate, which appears cartila- 

 ginous. 



3d. A cellular portion, which appears to contain a pellucid 

 fluid. 



4th. A thin membranous strip, which completes the septum 

 or partition. 



These parts may be distinguished from each other, when 

 magnifying glasses of sufficient power are used. 



The bony plate is composed of two lamina with small can- 

 celli between them, in which are canals for the transmission of 

 the fibres of nerves. These canals are extended into the carti- 

 laginous part. 



The membranous part which completes the septum is con- 

 tinued into the lining membrane on the surface of the cochlea. 



The bony portion of the scala does not extend towards the 

 apex of the cochlea so far as the cartilaginous and membranous 

 portions ; and none of them continue to the apex, for the lamina 

 spiralis terminates in the infundibulum before it has arrived at 

 the apex. Its extremity has the form of a hook, and is, there- 

 fore, termed Hamulus. 



As this septum does not extend to the apex of the cochlea, 

 the two scalae necessarily communicate with each other at the 

 apex. 



These different bands or strips which compose the lamina 

 spiralis, are called its Zones, and are termed Zona Ossea, Zona 

 Coriacea, Zona Vesicularis, and Zona Membranacea. 



