LORENZINl'S AMPULLAE. 



81 



two long canals which pass backwards and outwards on the dorsal side of 

 the fin ; the anterior of these anastomoses with the dorsal part of the 

 above described extension of the hyomandibvilar canal. 



The whole of this system of canals is in Elasmobranchs 

 supplied by the facial nerve and the lateralis branch of the vagus, 

 which probably belongs to the facial system (see account of 

 cranial nerves under Elasmobranchii and Fig. 41). 



The ampullary canals or Lorenzini's ampullae, are un- 

 branched canals (Fig. 43), opening, usually in groups, on the 

 surface of the head and ending internally in vesicles — the 

 ampullae — which are beset with radial dilatations (Fig. 44). 

 The ampullae are placed in groups, the position of which in 

 a typical case is shown in Fig. 41. 



Fio. 42. — Cephalic lateral line of Chimaera (from Gegenbaur). a lateral 

 groove of trunk, 6, c" infraorbital, c supraorbital groove, c' supraorbital 

 grooves ; passing back to join infraorbital ; x frontal appendage. 



The sensory epithelium is confined to the ampullse to which the 

 nerves, in all cases branches of the facial, are distributed. The 

 tubes and ampullae contain a gelatinous matter. 



Savi's vesicles are found in Torpedo round the electrical organs 

 They are completely closed. 



The pit organs, found in many Elasmobranchs are sense 

 organs sunk in pits on different parts of the head and trunk, and 

 are supplied by the facial nerve, the lateralis of the vagus, and 

 the trigeminal. 



In Teleosteans, Ganoids and Dipnoi the lateral line system 

 and the pit organs alone are present. The lateral line has an 

 arrangement very similar to that described for Elasmobranchs, 



Z— II G 



