266 AMERICAN TESTUDINATA. Part II. 



laginous, and in the Ophidians it is so elastic as to allow the branches to move 

 far apart one from the other. 



This solid conformation of the head shows, again, the high standing of the 

 Testudinata, for the loose connection of the bones of the head is a character peculiar 

 to Fishes, while the solid, compact skeleton of the head is characteristic of Mammalia. 

 There is still another feature in the head of the Turtles which gives it a general 

 interest: the great similarity of the hind part of the skull to a vertebra. The 

 resemblance of the os occipitale basilare to the body of a backbone, and of the 

 ossa occipitalia lateralia to an upper arch, is more striking than in any other Ver- 

 tebrate. The bones around the brain are flattened ; the parietal bones inclose 

 the brain from above and from the sides, the wings of the sphenoid remaining 

 relatively small. There are two pairs of frontal bones; the exterior ones are 

 generally, though not always, united by a median suture, and cover the nasal 

 cavity from behind. There are no nasal bones, except in one genus.^ In the 

 fresh animal, the condylus occipitalis is a nearly round prominence with a depres- 

 sion in the middle, in which the second vertebra articulates ; when dry it is 

 triangular. In the dry skull the composition of this condylus, formed from one 

 basilar and two lateral occipital bones, is evident by the sutures. This structure is 

 the same as in the true Saurians and Ophidians ; but while in Turtles the second 

 vertebra fits with its head into the pit in the middle of the condylus, in the 

 Saurians and Ophidians, on the contrary, it I'ides upon a roundish excavation 

 on the upper side of the condylus. Again, the Crocodiles differ from the three 

 other orders of Reptiles by having their round condylus formed only from the 

 OS basilare. 



There are nine vertebrae of the neck, (not eight as is generally stated,) the 

 second, the so-called odontoid process of the epistropheus, very clearly showing, in 

 these Eeptiles, its right to be considered as a distinct vertebra, as it remains separated 

 from the epistropheus through life. There are no transverse processes in any 

 vertebra of the neck. The upper arches are always soldered to the bodies of 

 the vertebrae by sutures. The articulation of these vertebrae to each other is 

 entirely peculiar to Turtles, there being some convex-concave, some concave-convex, 

 one biconcave, (usually the eighth,) and one biconvex, (usually the fifth.) This 

 configuration of the vertebrae gives fixity to certain bendings of the neck, thus 

 depriving it of that flexibility which is characteristic of the neck of the Birds, 

 while it is, at the same time, much more movable than the neck of any other 

 order of Reptiles, or that of the lower Vertebrates. 



^ In Hydromedusa, nasal bones liave been dis- Cheloniorum, Berol., 1838.) Whether this character 

 covered by W. Peters, (Observationes ad anatomiain is common to all Hydraspides, remains to be seen. 



