THE CHORDA TYMPANI. 165 



(3) communis fibres secondarily added to the r. mandibu- 

 laris V, or (4) a nerve distinct from any of the preceding. 

 Which of these nerves persists in a given case after the 

 obliteration of the spiracle is a matter which it may not 

 be possible to determine from the adult peripheral re- 

 lations, nor is it safe to assume that it is the same nerve 

 in all cases. 



The condition in Raja and Spinax is especially fruitful 

 in suggestions for the interpretation of higher forms. 

 Here Stannius describes ('49, p. 57) three branches of the 

 r. palatinus: 



1. A small posterior (caudal) branch, which supplies 

 the pseudobranch of the spiracle. This is manifestly the 

 proper r. pre-trematicus VII, /. e. , the nerve for the pre- 

 spiracular demibranch. 



2. The first anterior branch. A stronger nerve which 

 sends a twig back for the anterior lining of the spiracle, 

 anastomoses with branches i and 3, and then runs for- 

 ward and inward under the mucous lining of the mouth 

 between the hyoid and the mandible, reaching to the ven- 

 tral median line. This nerve perfectly fulfils every con- 

 dition for the chorda tympani, and is an independe^it nerve 

 for its entire length. 



3. There is, finally, the second anterior branch, or true 

 r. palatinus. 



We have in these fishes, then, a chorda tympani in 

 addition to the r. palatinus, the pre-trematic VII and the 

 post-trematic VII. 



Chimaera would seem from Cole's description ('96a, 

 p. 652) to present a simple and primitive condition. The 

 r. pre-trematicus VII arises from the base of the palatine 

 and distributes to the, ventral portion of the pharynx be- 

 hind the low^er jaw. This he calls (I think correctly) the 



