442 HENRY C. TRACY 



HISTORICAL SUMMARY OF THE LITERATURE ON THE EAR- 

 SWIMBLADDER RELATION IN CLUPEIDAE 



According to Weber's description (1820), the anterior end of 

 the swimbladder in Clupea harengus bifurcates and sends a small 

 diverticulum into each side of the head. It enters the occipital 

 region of the skull and passes anteriorly along a canal inside the 

 bones at the base of the skull, and ends in two expanded vesicles 

 each enclosed in a capsule of bone (globulus osseus). One of 

 these, the anterior, lies in the basilar part of the 'temporal' bone, 

 the other, in the lateral part of the 'temporal' bone. 



The anterior bony capsule is nearly filled by the membranous 

 bulla, but from the inner side it also receives a diverticulum 

 from the vestibule of the membranous labyrinth which extends 

 into it from the cavum cranii. The opening of the capsule, 

 through which this diverticulum of the vestibule enters, is a 

 large transverse fissure which opens into the cavum cranii. 

 Inside the bony capsule the air-filled membranous vesicle of the 

 swimbladder flattens against the surface of the distal end of the 

 diverticulum and fuses with it. By the apposition of these two 

 surfaces a septum is formed which stretches across the cavity 

 of the capsule like a tympanic membrane and divides it into two 

 parts. The edge of this septum is fixed to a 'cartilaginous' 

 ring which is attached to the inner surface of the capsular wall. 

 The posterior of the two bony capsules admits no diverticulum 

 from any part of the membranous labyrinth, but is entirely 

 filled by the membranous vesicle of the swimbladder. 



Weber believed that he demonstrated an endolymphatic canal 

 which runs under the brain and connects the vestibules of the 

 two sides, (subcerebral canal). He also noted that in these 

 fishes the wall of the membranous labyrinth is much thicker 

 than the same structure in other fishes. 



Breschet ('38) studied the ear-swimbladder relation in Clupea 

 alosa. He describes accurately, and in more detail than Weber, 

 the membranous labyrinth, the bony capsules, the cartilaginous 

 tubes which enclose the swimbladder diverticulum, and the 

 general relations of these structures to the rest of the skull. 



