THE SYRINX OF GALLUS DOMESTICUS 



179 



the vibrating membranes proper. This layer is composed of 

 numerous white and elastic fibers. It is to be noted that there 

 is a tendency for all layers to become much thinner as the tym- 

 panic membranes are approached (fig. 5). 



The external and the internal labia, which occur in song birds 

 in connection with the tympanic membranes, were not observed 

 in the chicken. 



The semilunar membrane is poorly developed in the chicken. 

 It is nothing more than a modification of the mucosa over the 

 cephahc border of the shaft of the pessulus. The epithelium in 

 this position is thickened and belongs to the stratified ciliated 

 colunmar type. The submucosa too, as already mentioned, is 

 especially thick. Thus it is evident that the semilunar membi ane 

 in the chicken is but a poor representative of this structure as 

 found in many song birds. 



II. DEVELOPMENT 



For this division of the present investigation the following 

 selected stages were used. 



Twenty-four hours after hatching. 



Serial cross sections were made of nearly all the stages and 

 serial coronal sections were made of a large number of the stages. 

 In the early stages series were made of the entire embryo whib 

 later only the syringeal region was sectioned. For the most 

 part the sections were cut ten micra in thickness. In the more 

 important stages a drawing of the embryo was made before sec- 

 tioning, which was utilized in obtaining the plane of sectioning 



