276 AMERICAN TESTUDINATA. Part II. 



in Saurians.^ The helix is a simple, round, membranous sac, with a closed fenestra 

 rotunda, and a communication with the saccus vestibuli by means of a membra- 

 nous canal. A very long columella is attached to the fenestra ovalis, which itself 

 is closed by an opercle. The cavitas tympani is divided into two parts by a 

 bony septum. The tunica tympani is only attached to the os quadratum. Between 

 the two lamellae of this membrane lies a cartilaginous plate, into which the colu- 

 mella is inserted. 



The Ei/e. This organ is larger in proportion and more movable in Turtles 

 than in other Rej^tiles.^ We find in the constitution of this organ a great similarity 

 with Birds. Not only are the protecting membranes of the eyeball in Turtles and 

 Lizards, in contradistinction to Snakes, very much as in Birds, there being two 

 eyelids and a membrana nictitans, but we find in Turtles also the same bony 

 framework in the cornea as in Birds. This bony ring has been erroneously ascribed 

 also to Crocodiles.^ It does not exist either in these, or in Ophidians, or in Sauri- 

 ans, but singularly enough we find it again in all those huge Reptiles of past ages 

 known as Plesiosauri and Ichthyosauri. The iris of Turtles is always colored, gen- 

 erally dark, but in some red, or even milk-white. We see, however, that this color 

 varies much in one and the same species, as, for instance, in Cistudo virginea, in 

 Ptychemys concinna, etc. The form of the pupil, which is vertical and elliptical in 

 many Snakes and Saurians and in all Crocodiles, is round in all Tui'tles, as it is in 

 Birds. There is, however, no pecten in the vitreous body, as in all Birds and in 

 many Saurians ; the vitreous body itself is very large. In the orbita we find two 

 well developed glands, namely, a lachrymal gland above the bulbus, and another, a 

 Ilarderian gland, behind and inside. 



The Nose. While the sense of seeing, and particularly that of hearing is 

 highly developed in Turtles, the sense of smelling is much less so ; and while the 

 former two senses exhibit in them a degree of perfection which we find elsewhere 

 only in warm-blooded animals. Turtles do not at all stand above the level of other 

 Reptiles with respect to the latter sense. In explanation of this we may perhaps 

 say that the slow rhythm of the respiration, which is common to all four orders 

 of Reptiles, does not facilitate the admission of odoriferous materials into the nose, 

 and that it is for this reason that we find the nerves and bones of this organ 



' In Dumt'ril et Bibron, Erpetologie generale, particularly in the structure of its heaJ, forms un- 



vol. i., p. 39'J, this membrane is erroneously said not questionably a family for itself. 

 to exist in Turtles. ' Already Soemmering, and later, Rymer Jones, in 



" There is one single exception to this statement ; Todd's Encyclopaedia of Anatomy and Physiology, 



in the Soutli-American Matamata, (Chelys fimbri- vol. iv., p. 314, have made this statement, which we 



ata,) the eyes are remarkably small. This Tur- must deny, in accordance with the observations of 



tie, however, so peculiar also in other respects, and Tiedemann, Stannius, and our own. 



