THE LATERAL SENSE ORGANS OF ELASMOBRANCHS. 489 



the two groups appeared as one, and the importance of the innervation in dis- 

 tinguishing between the groups of ampullae was demonstrated in a practical way. 



(3) Outer Buccal. 

 The outer buccal branch of the buccal nerve, after its division from the inner 

 buccal, proceeds direct to the outer buccal ampullae, passing through the antorbital 

 cartilage on its way (text-figs. 6 and 8). After the major portion of the nerve has 

 broken up for the supply of the ampullae, the remaining slender portion continues 

 forwards for the supply of part of the infra-orbital (sensory) canal. 



(4) Hyoid. 

 The large hyomandibular nerve proceeds direct, behind the spiracle, to the hyoid 

 group of ampullae, where it breaks up into numerous branches, some of which go to 

 supply the ampullae, and others to supply both the dorsal and ventral loops of the 

 hyomandibular (sensory) canal (text-figs. 6 to 9). 



(5) Mandibular Nerve. 



The mandibular branch of the hyomandibular nerve divides oft* from the main 

 stem before this splits up for the supply of its sense organs, and then, curving round 

 to the lower jaw, sends a short branch to the mandibular capsule, and a longer one 

 to the mandibular (sensory) canal (text-figs. 7 and 9). 



6. Comparison with other Members of the Batoidei. 



In closing this account it may be well briefly to compare the structure and 

 arrangement of the ampullary system in Raia with that of the most closely related 

 forms which have been described. These are Torpedo and Trygon — the only other 

 genera of the Batoidei of which accounts have been given. For details relating 

 to the former, reference has been made to Leydig's Rochen und Haie, Fritsch's 

 Torpedineen, and Coggi's Sviluppo delle Ampolle di Lorenzini. The ampullary 

 system of Trygon has been referred to nowhere except in Leydig's Rochen und 

 Haie, where very brief allusions are introduced among references to many other 

 Selachians. 



According to Leydig, Torpedo has the simplest ampullae, and he describes them 

 as simple round vesicles without outward sacculations, although internally four- 

 chambered by means of partitions. He describes the only two pairs of ampullary 

 groups which he recognised as being enclosed in capsules. 



According to Coggi's more recent account of Torpedo ocellata, there are three 

 pairs of groups of ampullae, comprising 168 ampullae in all, and supplied respectively 

 by the superficial ophthalmic, the buccal, and the external mandibular branches of 

 the facialis. Of these groups the mandibular contains by far the largest number of 



