68 
ON THE PHYSIOONOMY OF SEEPENTS. 
number, are attached. The choroid, of a more close tex- 
ture, has its two surfaces covered by a dark pigment. The 
membrana Ruyschiana is well developed. The iris has a 
considerable breadth; the colour varies in the different 
species. The retina, tolerably thick, has nothing peculiar. 
The lamellar structure of the vitreous humour of serpents 
has only lately been demonstrated.^ The crystalline lens, 
of a spherical form, is more than half buried in the vitre- 
ous humour, which is not large. 
OE THE EAE. 
The structure of the ear demonstrates that Ophidians 
have the sense of hearing more dull than most of the 
class Amphibia. The small bone of the ear being buried 
in the flesh, implies the total want of a tympanum, and 
hence it follows that the sounds can only penetrate to the 
organ of hearing, when they cause vibration of that thick 
cuirasse which forms the general integument of Ophidians. 
This small bone, called by Cuvier the stapes, although in 
fact it represents the three bones of the ear in animals of 
a higher rank, is in the form of a thread, which usually is 
prolonged from one side to the articulation of the lower 
jaw, while the other end is enlarged into a disk, to shut 
the fenestra ovalis. Immediately behind that entrance to 
the exterior ear, another aperture is found, representing, as 
has been stated by M. Windischmann, the fenestra orbi- 
cularis. The same philosopher has observed, that the 
structure of the internal ear of the Ophidians approaches 
to that of all the Saurians which he has examined ; that 
is to say, in them is formed an organ of an oval form, 
called the cartilaginous ring, destined to receive the nerve 
of hearing, which is distributed on its surface. This nerve 
forms on one side a very considerable enlargement, called 
Lagena, because the figure of this part resembles a bottle. 
See WiNDiscHMANN, PI. 2, fig. 12, for the internal organs 
of hearing in the Dipsas, 
* See the excellent Anatomy of the Python ivith-two-Rays, published 
by Retzius, Isis, 1832, p. 512. . 
