The Latero-Sensory Canals and Eelated Bones in Fishes. 



447 



posterior half by the epiotic (exoccipitale), suprascapular and lateral 

 occipital. The ventral wall of the pit, the wall that alone separates 

 the pit from the pharyngeal cavity, is very thin throughout a larg-e 

 part of its extent, this thin portion lying ventro-mesial to, and being- 

 enclosed within, the arch of the horizontal semicircular canal of the ear. 

 The pit consists of two portions, a larger external and a smaller 

 deeper one, the latter portion forming a pit -like depression in the 

 bottom of the larger portion. A large opening in the posterior wall 

 of the pit-like depression leads backward into a large recess which is 

 separated from the larger external portion of the pit by a thin shelf 



CSsŒ 



sic 



ESC 



toc 



---cse 



Cut 1. 



Diagrammatic transverse section of the acustico-temporal pit of Gymnarchns. showing 



the relations of the sacculus to the supratemporal latero-sensory Canal. 



of bone. This recess lodges the lenticular- shaped lagena of the mem- 

 branous ear, with its enclosed otolith, the pit-like depression lodging 

 a small inner portion of the sacculus, that portion of the sacculus 

 containing the macula ac. sacculi, and enclosing the saccular otolith. 

 This inner or deeper portion of the sacculus is connected with the 

 lagena by a short, small tube, and with the utriculus by a similar 

 tube which traverses a small foramen in the bottom of the pit-like 

 saccular depression. The remaining, larger, external portion of the 

 pit is almost completely filled by a large, balloon-like distension of 

 the non-sensory portion of the sacculus, which projects upward to the 

 level of the mouth of the pit and there lies closely against a delicate 

 membrane which alone separates it from the supratemporal, and ad- 



