CEANIAL NERVES OF CAECILIANS 555 



Despite the conflicting testimony of observers and the vary- 

 ing relations of the structural parts, the main cervical sympa- 

 thetic chain in the caecilians may be said to consist typically of 

 two ganglia connected anteriorly with the Gasserian and genicu- 

 late ganglia, and related by anastomoses with the IX-X com- 

 plex and the anterior spinal nerves. The anterior sympathetic 

 ganglion occurs usually at a level slightly posterior to the root 

 of the occipital nerve. It may or may not be closely related to 

 the trunk ganglion of the vagus. The second sympathetic gan- 

 glion is situated at a level between the roots of the second and 

 third spinal nerves. Its frequent intimate relation to the second 

 spinal nerve is to be regarded as largely incidental, although in 

 effect a ramus communicans thus may be estabhshed. 



GENERAL STATEMENTS 



For one in search of primitive anatomical characters in the 

 caecilians a study of the nervous system gives little comfort. 

 The impression gained, rather, is that we are dealing here with 

 highly specialized animals. 



In the nervous system of the caecilians the amphibian type is 

 overwhelmingly dominant, but with modifictions, these modifi- 

 cations not being in the direction of supposedly ancestral sim- 

 plicity. The double condition of the olfactorius; the occurrence 

 of two ganglia upon the trigeminus; the separation of a second 

 branchial ganglion, as the writers are inclined to interpret the 

 root ganglion upon the vagus, from the other vagal ganglia; 

 these which may be interpreted as primitive characteristics the 

 writers look upon as incidental exaggerations of conditions 

 characteristic of amphibians in general. 



The absence of structures characteristic of other amphibians 

 is more striking than the presence of supposedly primitive char- 

 acters. The mode of life of the caecilians necessitates the ves- 

 tigial condition, or even absence of certain structures, as the eyes 

 and associated parts and the limbs and related muscles. But 

 quite unrelated to such modifications are the absence of 1) a 

 ramus pretrematicus IX; 2), a Jacobson's commissure; 3) a 

 'ramus communicans' between glossopharyngeal and facial 

 nerves; 4) a ramus auricularis X; 5) an anastomosis between the 

 ramus ophthalmicus profundus V and the ramus palatinus VII. 



