82 



CLASS PISCES. 



^ 



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

 ing ampuUary tubes (from Gegenbaur). iyf 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 tubules, 

 which are iji 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, Gohius, 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 tlie 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 

 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 vagu& 



Fig. 44. — Lorenzini's am- 

 pulla. A from the side 

 with nerve n and portion 

 of tube c ; B in section 

 (from Gegenbaur). 



