Chap. I. 



ORGANS OF SENSES. 



275 



Birds than of other Reptiles, in which hitter the organs of locomotion are never 

 confined to the legs alone. See above, p. 253. 



The characteristic features of the N. sympathicus' are only to be appreciated 

 by a minute comparison of all its original roots, anastomoses, ganglia, etc., with 

 those of Crocodiles, Lizards, and Snakes. But, though there are many differences 

 in its conformation in these different orders of Reptiles, we do not deem it 

 necessary or useful to enter into the details of such a comparison ; in the first 

 place, because only some two or three species of Turtles have as yet been inves- 

 tigated with special reference to that nei've, so that there w^ould be danger of 

 confounding ordinal with family or even generic characters; and in the second 

 place, because the diflerences which we have noticed do not show an inti- 

 mate connection with the whole nature of the Turtles, in contradistinction to 

 other Reptiles. It is, moreover, proper that in Comparative Zoology we should 

 introduce only such anatomical characters as are understood in their connection 

 with the whole nature of the animals under consideration. Other anatomical 

 details would be useless for the zoologist. 



SECTION IX. 



ORGANS OF SENSES. 



The Ear. There is no movable external ear as in the Crocodiles ; but in all 

 Testudinata we find a cavitas tympani and a membrana tympani, which are wanting 



* The N. sympathicus begins in Turtles as jilexus 

 spUenoidt'us, and is connected with the second branch 

 of the N. trigeminus. It runs as a siinple trunk back- 

 wards, gives brandies to the nose, and receives 

 branches from tlic N. abducens facialis ; then after 

 pa.ssing through the os petrosum as N. Vidianus it 

 receives branches from the N. facialis and glosso- 

 pharyngeus, then from the N. vagus and hypoglossus, 

 and then runs as one superficial stem along the neck 

 to the thorax, connected by branches with the nerves 

 of the neck. Then taking np brandies of the vagus, 

 it forms the ganglion thoracicum primum, which 

 sends its threads to the plexus cardianus and pul- 

 monalis. Then the string forms several swellijigs, 



connected with the ple.xus brachialis, forming several 

 loops which unite again into ganglia and communi 

 cate with the anterior brandies of the spinal nerves. 

 Then after giving branches whidi go to the inter- 

 costal nerves, it forms again two plexus, the first 

 sending branches to the stomach, and accompanying 

 the arterla ('(rliaea ; from the seeonil jiiixus originate 

 branches for the intestines, and others for the kidneys 

 and the generative organs. See St.vxxiis, Lehrbuch 

 der Vergleichenden Anatomic der Wirbelthiere. Ber- 

 lin, 1846, p. 192-93; Bojanus, Anatome Testudinis 

 P>uropa*a', PI. xxii. and xxiii. ; and Swan, Ilhistra- 

 tions of the Comparative Anatomy of the Nervous 

 System, London, 1841, PI. xv. and xvi. 



