68 ON THE PHYSIOGNOMY OF SERPENTS. 



number, are attached. The choroid, of a more close tex- 

 ture, has its two sui'faces 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. 



or THE EAR. 



The structure of the ear demonstrates that Ophidians 

 have the sense of hearing nun-e 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 wiiich forms the general integument of Ophidians. 

 This small bone, called by Cuvier the stapes, although m 

 fact it represents the three bones of the ear in animals of 

 a higher rank, is in the form of a thread, Avhich 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, w^hich 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, PL 2, fig. 12, for the interaal organs 

 of hearing m the Dipsas. 



* See the excellent Anatomy of the Python with-two-Rays, published 

 by Retzius. Isis, 1832, p. 512. 



