82 



CLASS PISCES. 



FIG. 43. A portion of the snout of Scyllium in section, show- 

 ing ampullary tubes (from Gegenbaur). N nerve ; a ampullae ; 

 c epidermis ; t tubes ; c' dermis ; o openings of the tubes ; 

 a' passage of a tube through the dermis. 



but the canal wall is sometimes ossified, especially on the head, 

 and the ossifications may be fused with the dermal and cranial 

 bones. Very often the canal traverses the scales and bones, and 



the sense organs 

 are contained in 

 the osseous tissue. 

 In such cases the 



lateral tubu les, 

 which are in some 

 cases branched, 

 their openings 

 forming so-called 

 cluster pores, per- 

 forate the bone, 

 as does the nerve 

 going to the sense 



organs. In this way certain scales on the body and bones of the 



head may acquire a special relation to these organs. Pit organs 



are present both on the trunk and head and often lie along the 



course of the main canals. In a few cases (Esox, Gobius, Liparis, 



etc.) the cephalic canals are alone present, the sense organs in 



the trunk being isolated and not connected by a longitudinal 



canal. In a few cases the longitudinal canal 



may have the form of a groove for a part 



of its extent. The openings of the lateral 



tubules may occur between the scales as 



well as upon them. 



In addition to the innervation found 



in Elasmobranchs the glossopharyngeal 



frequently sends a branch to a few of the 



posterior cephalic sense organs ; and it has 



been stated that the ophthalmicus super- 



ficialis trigemini also takes part, but this 



must be regarded as doubtful. In any 



case the nerves innervating this system of 



lateral line sense organs can always be FIQ 



traced to the special centre in the brain 



from which the auditory nerve arises. The 



pit organs are innervated by the trigemi- 



nal as well as by the facial and lateralis of the vagus. 



44. Lorenzini's am- 

 pulla. A from the side 

 with nerve n and portion 

 of tube c ; B in section 

 (from Gegenbaup). 



