536 FRANCIS VILLY. 
through the foramen rotundum is not described, and the close 
relation of both to the parts of the cochlea is not noticed. I 
have investigated the course of these canals in the common 
frog, the toad, and Dactylethra larva. 
In Rana temporaria the system is composed of two 
canals in the hinder part of the ear, closely connected with 
the cochlea and communicating with each other within the 
skull. The walls consist of a single layer of much flattened 
cells, and backing this layer there are a few scattered cells 
lying in the perilymph. These walls are distinct though thin 
at all points in the course of the canals, which therefore do 
not communicate with any other system. 
The first canal to be described, the ductus perilymphaticus, 
is in close relation with the lagena. The walls of the extre- 
mity of this part of the cochlea are very different on the inner 
and outer surfaces, i.e. those looking towards and away from 
the brain respectively. The outer wall is thickened and bears 
sensory cells, and it is strongly curved with the concavity 
towards the brain. The opposite or inner wall is flat and 
exceedingly thin, consisting of a layer of very flat pavement 
cells, and against this flat part abuts the perilymphatic canal. 
This canal can be traced downwards and backwards as far as a 
foramen in the inner and hinder part of the floor of the cap- 
sule. Through this foramen it passes and lies between the 
pharynx and the base of the skull. Here it expands some- 
what (saccus perilymphaticus), though it is spacious through- 
out its course, and from this point it extends backwards some 
distance, even behind the foramen of the glossopharyngeal 
nerve. Just in front of this nerve a duct, somewhat narrower 
than any part yet described, passes up from the perilymphatic 
space through the foramen along with the nerve, and enters 
the skull. Its connections within the skull will be de- 
scribed below. The second canal has relations with the pars 
neglecta of the cochlea, just as the first has with the 
lagena. It is applied to the flattened wall of this pouch from 
below ; besides this part in immediate connection with the 
cochlea, there is a spacious continuation of it within the cap- 
