104 



ZOOLOGY 



SECT. 



to be looked upon as a spinal nerve which has become included in 

 the cranial region : even in some Fishes it passes out through 

 the skull. 



The sympathetic nerve (sym.) is continued into the head and 

 becomes connected with certain of the cerebral nerves. 



FIG. 790. A, Sensory canals of the left side of the head of a Bony Fish, showing the supra- 

 orbital (s.o.), infra-orbital (i.o.), operculo-mandibular (op.m.), and lateral (I.e.) canals. (From 

 the Cambridge Natural Hisiory, after Cole.). B, organ of the lateral line (neuromast) in a tailed 

 Amphibian (semi-diagrammatic), a. epidermic cells, through which are seen b, sensory 

 cells ; c. sensory hairs ; N. nerve ; R. hyaline tube. (From Wiedersheim's Vertebrata.) 



Sensory Organs. The whole surface of the body forms an 

 organ of touch, but special tactile organs are more or less widely 

 distributed. End-buds consist of ovoidal groups of sensory cells 

 supplied by a special nerve : touch-cells (Fig. 789, A) are nerve-cells 

 occurring in the dermis at the termination of a sensory nerve : touch- 

 corpuscles (B) are formed of an ovoidal mass of connective-tissue 

 containing a ramified nerve, the terminal branches of which end 



