3G2 AMERICAN TESTUDINATA. Part II. 



SECTION X. 



ON THE BRAIN OF THE DIFFERENT FAMILIES OF NORTH AMERICAN TURTLES. 



In the description of the families of Testudinata, given in the preceding sec- 

 tions, only such structural features have been considered as bear directly upon 

 the form of the animal. It would, however, be very interesting to ascertain 

 further, how far the form of all the different organs is also characteristic of 

 families in general, especially since it has already been shown that the devel- 

 ojDment of some of the organs,^ at least, has an immediate influence upon the 

 form of the body; but I have thus far refrained from making such an inves- 

 tigation, as it would require more extensive comparisons than could properly 

 be introduced in this part of my work. Yet, as I knew, from dissections made 

 upon a large scale, many years ago, that the form of the brain is characteristic 

 of the different families of Fishes, I have thought it desirable to extend these 

 comparisons to the Testudinata, in order not to leave the subject entirely out of 

 sight. The result of this comparison coincides fully with that obtained in the 

 class of Fishes. It stands proved, that while the form of the brain has no 

 immediate bearing ujion the form of the skull ^ and of the head in general, it 

 is yet typical in every family. 



All Turtles agree among themselves veiy remarkably in the structure of the 

 brain. From the large hemispheres, the transverse diameter of which is about 

 equal to one half of its whole length, the brain grows narrow forward and 

 backward. The relations of the different parts of the brain are remarkably 

 constant in the whole order of Testudinata ; so much so, that, of all the organs, 

 the brain seems the least likely to undergo deeper modifications in one and the 

 same group, and therefore to be not only one of the most important organs 

 of the Vertebrata, but also one of the most characteristic, in a zoological point 

 of view. However much the Turtles may assume, in their external organization, 

 characters of the higher Vertebrata, (of Birds and Mammalia, for instance,^) still, 

 in relation to the brain, they preserve fully the Reptilian character. Their brain 

 remains slender and long. This fact is very striking when we compare the head 

 of a Turtle with that of a Mammal or that of a Bird.'' The skull of a Turtle 



1 See Chap. 1, Sect. 11, p. 282. « Comp. Chap. 1, Sect. 18, p. 308-312. 



^ This result is in glaring contradiction with the '' In these, the brain-box is much more distinct 



doctrines of Phrenology. from the bones of the face and jaws than in Turtles. 



