THE CLUPEOID CRANIUM AND THE SWIMBLADDER 469 



cannot be true that the two chambers of the capsule are formed 

 by processes of the basisphenoid bone, as Tysowski has assumed, 

 and therefore his whole morphological theor}^ falls to pieces. 

 This conclusion is substantiated by de Beaufort's observations on 

 the embryology of the precoelomic diverticulum. His figures 

 show that the anterior membranous vesicle actually develops 

 inside of the chondrocranium immediately under the mem- 

 branous labyrinth. This agrees with my previous published 

 statements, regarding the developing stages of Stolephorus 

 mitchilH (Tracy, '11). 



It is another question to explain the anterior bony capsule as 

 "ein Erzeugnis der Prootica" in view of de Beaufort's obser- 

 vation that the bony capsule is formed by a process of bone 

 development from the connective tissue surrounding the mem- 

 branous vesicle. 



Tysowski questioned Ridewood's identification of the so-called 

 'posterior wings of the parasphenoid' as a part of the para- 

 sphenoid bone. Relative to this, it is pertinent to refer to one 

 of the most characteristic morphological features of the teleostean 

 skull, viz., that the parasphenoid wings form the walls of all 

 except the upper part of the eye-muscle canal. The para- 

 sphenoid wings in Clupeoids conform to this relation. It can 

 easily be seen in dissections, and also in cross-sections of the skull, 

 that the rectus eye muscles arise along the whole medial surface 

 of these wings as far back as their extreme posterior end. There 

 is nothing to indicate that these wings differ in any essential 

 respect from the corresponding bones in other fishes, except in 

 their unusual ventral and posterior extension. ^ 



Tysowski's denial of the existence of the auditory foramen 

 (which is described in all previous papers on the clupeoid skull) 

 is also probably without substantial basis. It is true that on 

 careful dissection a thin scale can be demonstrated over this 

 foramen, but it is transparent and does not resemble bone in 



1 Tysowski compares the wings of the parasphenoid bone with the processus 

 pharyngealis in Ostariophysae. Sagemehl ('91, p. 516) has suggested that the 

 processus pharyngealis is formed by the ossification of a ligament passing from 

 the posterior end of the base of the skull around the aorta to the swimbladder. 



JOCRN-AL OF MORPHOLOGY, VOL. 33, NO. 2 



