46 



BRAIN AND BODY OF FISH 



had any auditory function so that a new terminology was given to 

 them, the tripus, scaphoid, and claustrum. But we have now 

 returned to Weber and it has been proved that his views are correct. 

 At the hinder end of the anterior vesicle we have noted the 

 ductus communicans and here we have the representative of the 

 Eustachian tube as it controls the gaseous pressure in the middle 

 ear. The posterior sac as we have aheady stated was primitively 



— Canalis communicans. 



— Posterior cavity. 



■ — Scaphoid and Claustrum. 



— Intercalarium. 

 — Vertebral column. 

 — Tripus. 

 — Central plate. 

 — Tensor tripodis. 



— Membrana flaccida. 

 £.C — External coat of A.S. 



• — Anterior sac. 

 ^^ ■ — Posterior attachment of A.S. 

 1)0. — Ductus communicans. 

 S — Sphincter. 

 ^^ — Pneumatic duct. 



— Posterior sac. 



Fig. ii. 

 Dorsal view of swim-bladder and Weberian Ossicles of Carp. 



a lung and this is connected with the gullet by the pneumatic duct, 

 which corresponds to the larynx and, just as the larynx is guarded 

 by the epiglottis with its taste-buds, so the pneumatic duct is 

 guarded by its ring of sentinel buds. 



There are many other interesting details which make this com- 

 parison of the organs of hearing in man and fish very striking. We 

 may mention two : The tripus or malleus of a fish is kept tense 

 by a small muscle, by which it is attached to the central plate, and 

 in the human ear there is a small muscle that controls the malleus, 

 the tensor tympani. The outer wall of the anterior vesicle in fish 



