274 AMERICAN TESTUDINATA. Part II. 



SECTION VIII, 



NERVOUS SYSTEM. 



With reference to the brain, we may single out as characteristic of the Testudi- 

 nata tlie well developed hollow hemispheres, which are larger in j^roportion than 

 in other Reptiles, especially when compared to the lobi optici. Their surface is 

 generally smooth, but in some it is provided with a longitudinal fold. Their 

 cavities are continued into the hollow roots of the olfactory nerves. The cere- 

 bellum is relatively larger than in Ophidians and Saurians, yet smaller than in 

 Crocodiles. A longitudinal furrow divides it into halves. Between the two hollow 

 lolji optici and the hemispheres, there are two lol:)i ventriculi tertii, which give rise 

 to the optic nei'ves. Behind the large cerebellum follows a large vascular body, 

 (plexus chorioideus,) which lies upon the sinus medidlaj ablongata?.^ 



In relation to the nerves that originate from the brain and the meduUa 

 ablongata, we notice that, as in Ophidians and Saurians, the uervus hypoglossus 

 receives roots from the spinal marrow, which is not the case in Crocodiles. As 

 in Saui'ians and Ojihidians, the nervus vagus and the glossopharyngeus have always 

 each a root for itself, and, as in Saurians, each also a distinct passage through 

 the OS occijiitale laterale ; while in Ophidians there is only one passage, and in 

 Crocodiles, with some exceptions, only one common root for both those nerves, 

 which thus form also only one common ganglion. As in all Reptiles, the largest 

 nerve is the nervus trigeminus ; it is larger even than the nervus vagus, though 

 this latter is more developed in Turtles than in other Reptiles. 



The spinal marrow is rather thin along the middle of the body ; and the nerves 

 which originate in this region are very small, as there is not much room for 

 their function, in consequence of the immovability of that part of the trunk which 

 corresponds to the shield, and wliich moreover is covered by a thick, hard, horny 

 roof So much the larger, however, appear the two swellings of the spinal marrow 

 in the shoulder and pelvis region, where the legs, which in this oi'der of Reptiles 

 have to support and to move the whole body, are to be provided with nerves. 

 Thus the size of these swellings, when compared with the general diameter of the 

 spinal marrow, is characteristic of the Testudinata, and more resembles that of 



* For the differences of the brain in different the whole nervous system of the European Emys has 

 families, see below under the head of The Family been given by Bojanus, in his Anatome Testudinis 

 Cliaracters. A beautiful illustration of the brain and Europrea% PI. xxi.-xxiii. 



