364 



AMERICAN TESTUDINATA. 



Part II. 



pointed angle. This contraction is greatest in the Cinostenioida?, less in Chelydroidse, 

 Trionycliida3, and Emydoida?. The hind part of the ventricle, which follows the con- 

 traction, is very long in Trionychida?, Cinosternoidte, and Chelydi'oidas, but less so in 

 Emydoidaj. In land Turtles, the ventricle is very wide ; the contraction in the mid- 

 dle is nearly wanting, and the whole is very short. In relation to this ventricle, 

 Cistudo shows again beautifully its standing as the highest among the Emydoidse, 

 and next to Testudo. Its ventricle is broader and shorter than in any other of 

 the Emydoida?. The lobi olfactorii are generally very much developed in Turtles, 

 and the nervi olfactorii rather strong. They are, however, different in different 

 families: longest and most slender in sea Turtles, very short and strong in land 

 Turtles, more slender again in Chelydroidaj, Cinosternoida3, Trionychidse, and Emy- 

 doida3. Accordingly the cavity of the nose also is very large in the herbivo- 

 rous land Turtles, smaller in Chelonii proper, as well as in Emydoidoe, Cinoster- 

 noidae, Chelydroidae, and smallest in TrionychidiB,^ in which the sense of smelling, 

 in spite of that long, protracted proboscis, seems very little developed, as is gen- 

 erally the case in aquatic animals. In Testudo, and in Chelonii proper, the hemi- 

 spheres and the nervi olfactorii lie in a thick cartilaginous trough, which extends as 

 fir as the nasal cavity. This trough is very broad and rather short in Testudo; 

 narrow and long, on the contrary, in Chelonii proper, according to the propor- 

 tions of the lobi and of the nervi olfactorii. In all the other Turtles that trough 

 is much thinner ; in some, as in Cinosternoida?, it is little more than a stiff 

 membrane. This trough is in fact nothing but a part of the cartilaginous skull- 

 box, which remains vmossified throughout hfe. We find also some marked differ- 

 ences in relation to the nervi optici. In Trionychidas, the two nerves joierce the 

 trough, mentioned above, very near together, so as nearly to touch one another ; 

 on the contrary, in Testudo the nerves separate widely before they run through 

 the skull-box, and the distance between the two holes through which they pass 

 is about as great as the breadth of the lobi olfactorii above them. In Cinos- 

 ternoidae and Emydoidse (including Cistudo) we find the holes for these nerves 

 as near together as in Trionyx; in sea Turtles only they are more distant, 



^ The whole of that long, protracted nose so char- 

 acteristic of the Trionychidaj, is not so much an 

 organ of smelling (as the proboscis of some Mamma- 

 lia, the South American Nasua, for instance) as an 

 organ of respiration, and probably also of touch. 

 These Turtles, while lying in shallow water, stretdi 

 out their nose from time to time to the surface of the 

 water for the sake of breathing; but under the water, 

 when moving in the mud, this long proboscis has very 



liki^Iy a similar function to the long, protracted pro- 

 boscis of the Shrews and Moles, when burrowing 

 under ground, and groping for worms and larvte of 

 Insects. Trionyx may find its food in the same way, 

 which consists in mud shells (as Paludinas and Ano- 

 dontas) and larvae of Neuroptera, by feeling about 

 with its proboscis. Its fleshy lips, the use of which 

 is not yet known, may help in the search, as they 

 are movable. 



