THE CLTJPEOID CEANIUM AND THE SWIMBLADDER 441 



The first of these types as it exists in different species has 

 been described by various observers from the point of view of 

 gross structure. The third type, that is, the Weberian appa- 

 ratus, has been thoroughly investigated and, on its anatomical 

 side, is comparatively well known. 



Our knowledge of the second (i.e., the clupeiod) tj^e of the 

 ear-swimbladder relation has not greatly advanced since the 

 work of Breschet ('38). Tysowski ('09) and de Beaufort ('09) 

 are the only investigators to apply modern methods to the 

 study of this mechanism. De Beaufort's work, however, is 

 concerned with the whole group of Malacopterygii, and he re- 

 ports little that is new regarding the essentials of this structure. 

 Tysowski's paper is brief, and although it considerably advances 

 our knowledge of certain features of the ear-swimbladder rela- 

 tion in Clupeoids, it contains certain morphological conceptions 

 which are based on inadequate knowledge of the cranial struc- 

 tures in these fishes. 



This investigation has been undertaken for two reasons, 

 namely, that the American Clupeiods have been little studied 

 and that many elementary features in these structures seem to 

 be stiU matters of controversy. This paper will deal only with 

 the bony structure of the skull in its relations to the swimbladder 

 diverticulum and the membranous labyrinth. Certain details 

 regarding the relations of the cranial nerves to these structures 

 are also described. 



Upon investigation it was found that the ear-swimbladder rela- 

 tion is essentially the same in aU of the American Clupeoids 

 examined. Therefore, in this paper, those parts of the cranium 

 related to the swimbladder and the membranous labyrinth are 

 described as found in a representative American species (Pomol- 

 obus pseudoharengus) , with only incidental reference to the 

 other members of this group. Another paper, soon to follow^ 

 will describe the membranous labyrinth and its relations with 

 the swimbladder diverticulum. 



The drawings for this paper were made by Mr. Leo Masso- 

 pust, the department artist at Marquette School of Medicine. 



