282 THE DOG-FISH. 



of some kind. The nerves supplying them in the head are the 

 ophthalmic, buccal, and external mandibular branches of the 

 seventh nerve. 



Squeeze the head of a fresh specimen, so as to make the 

 gelatinous matter exude, and so render the openings visible. 



Bemove the skin from the dorsal and ventral surfaces of the 

 liead, an operation much facilitated by dipping the head into 

 Jiot water for a few moments : identify the masses of ampullce 

 and the nerves in connection with them, and trace the tubes 

 outwards and backwards to their openings. Some of the tubes 

 tvhich run alo'ng the dorsal surface of the skull, between the 

 cranium and the orbit, are some inches in length. 



Cut out a smallpiece of the mass of ampullm : put it on a 

 slide in a drop of luater : separate tlie parts with needles : 

 cover, and examine under the microscope. Note the ampulla, 

 their internal divisions, the nerves supplying them, and the 

 tubes. 



