118 



unites with a corresponding portion from the canal of the opposite 

 side , and thus forms the temporal commissure ; the trunk portion 

 runs backwards from the outer end of the commissure to terminate on 

 a level with the end of the vertebral column, after making a characte- 

 ristic bend above the lower lobe of the caudal fin. 



The precommissural part receives two branches of the lateralis 

 nerve, and gives ofi" five tubules. The temporal commissure receives 

 sixteen branches (eight from each lateralis nerve) and gives off sixteen 

 tubules; while the trunk or main part of the lateral canal receives 

 numerous branches from the lateralis nerve as it passes backwards 

 along the trunk and tail. 



The paper concludes by referring to the views held as to the 

 function of the sensory canals, and to some of the modifications of the 

 sensory canals found in Elasmobranchs. 



Amongst other things it is pointed out that in some cases e. g. 

 Heptanchus , the greater extent of the lateral canal is represented by 

 a furrow; while in other cases, e. g. Alopias, the canal system is more 

 elaborate than in Laemargus , the lateral and other canals giving off 

 numerous long branching tubules ; and that while in the comparati- 

 vely inactive Torpedoes the canal system is feebly developed — the 

 ventral canals being either absent or in a vestigeal condition, — in the 

 active Myliobatidae it reaches an enormous development , partly by 

 the folding of the canals , but chiefly by the dichotomous division of 

 both the dorsal and ventral tubules. 



3. The lateral sense organs of Elasmobranchs. II. The sensory canals of 

 the common Skate, Raia batis. 



By J. C. E wart, M.D., Regius Professor of Natural History, and J. C. Mitchell, 

 B.Sc, University of Edinburgh '. 



eingeg. 20. Januar 1892. 



In this paper it is pointed out that the lateral sense organs of the 

 Skate consist of 1) Sensory Canals, 2) Ampullary Canals, and 3) Sen- 

 sory Follicles. 



The sensory canals, the only structures dealt with in detail, have 

 the same general arrangements and are related to the same nerves as 

 in Laemargus \ the supra-orbital, infra-orbital and hyo-mandibular 

 canals being related to the superficial ophthalmic , buccal and hyo- 

 mandibular divisions of the facial respectively, and the lateral canal 

 to the lateralis division of the vagus. But while the canals of Raia 



1 Abstract of a paper communicated to the Edinburgh Royal Society. Decem- 

 ber 1891. 



