116 



2. The lateral sense organs of Elasmobranchs. I. The sensory canals of 



Laemargus. 



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



Edinburgh i. 



eingeg. 20. Januar 1892. 



In Elasmobranchs the lateral sense organs are represented by two 

 systems of canals and by minute sensory follicles. The canals which 

 open by numerous tubules on the surface of the skin, are in this paper 

 spoken of as sensory canals, while those which give off neither tubules 

 nor branches and are dilated at their proximal ends , are designated 

 arapullary canals. 



The general and comparative anatomy of the sensory canals of 

 sharks and rays has been, during recent times, studied under the 

 direction of Agassiz, first by Wilder and afterwards by Gar man. 

 The object of this investigation was chiefly to determine the value of 

 the canals in classification. Studying the canals from this point of 

 view has led to names being given to the canals irrespective alike of 

 their innervation and development , with , amongst other results , the 

 introduction of a somewhat arbitrary and complex nomenclature, and 

 the breaking up of what is from certain points of view a single canal 

 into several canals. 



For example, the canal which is innervated by the ophthalmic 

 division of the facial , consists, according to the Agassiz-Garman 

 nomenclature , of three canals ; while the canal related to the buccal 

 division of the facial is described as six canals. In this paper the re- 

 lations of the canals to the orbit, rostrum etc., have been regarded 

 as of secondary importance, while special attention has been given to 

 their innervation. Taking into consideration that the sensory canals 

 seem to be developed, and from first to last continue, in connection 

 w ith certain cranial nerves, it seems to me that the only logical way of 

 dealing with them is to regard as all important their development and 

 innervation. 



This plan has already to a considerable extent been followed by 

 Allis in his able paper on the lateral line system of A??iia; and it is 

 one which will , I venture to think , commend itself to future workers 

 on the lateral sense organs of fishes. 



According to this method there are altogether only four main sen- 

 sory canals in Elasmobranchs , viz: the supra -orbital, infra - orbital, 

 hyo-mandibular and lateral. All these canals are related to two nerves, 



Abstract of a paper communicated to the Edinburgh Royal Society, July 1891. 



