SENSE-ORGANS OF THE INTEGUMENT. 



165 



backwards the organs are arranged in metameric order, and, 

 always connected by longitudinal nerves, extend along the sides 

 of the body to the caudal fin in one or more "lateral lines" 

 (Fig. 133); they are thus often spoken of as organs of the 



FIG. 134. DIAGRAM SHOWING THE DISTRIBUTION OF THE SENSORY ORGANS OF 

 THE LATERAL LINE IN FISHES. 



a, supra-orbital,' and b, infra-orbital, portion ; c, mandibular, d, occipital, and e 

 lateral portions, the latter extending backwards along the sides of the trunk and 

 tail. 



FIG. 135. ORGAN OF THE LATERAL LINE OF A URODELE. (Semidiagrammatic. 



a, a, cells of the epidermis, through which the neuro-epithelium, b, b, can be seen ; 

 c, the terminal hairs of the latter (the peripheral Cecils are not represented) ; JR, the 

 hyaline tube ; N, the nerve-fibres passing to the* sensory cells. 



lateral line. The portions lying in the region of the head are 

 innervated by the trigeminal, while the lateral line is supplied by 

 (Compare p. 158.) 



the vagus. 1 



1 The development of the lateral branch of the vagus has not yet been 

 satisfactorily made out : it either grows backwards from the vagus ganglion, or, as 

 most authors maintain, it arises by a proliferation or differentiation of the deeper 

 layer of the epidermis in situ. 



In Anguilla, Gymnotus, and Ceratodus, the lateral nerve is represented by a 

 branch of the facial. 



