THE SYRINX OF GALLUS DOMESTICUS 171 



faces, like the lateral surfaces of the shaft of the pessulus with 

 which they are continuous, form the medial walls of the cephalic 

 ends of the bronchi, while the cephalic portions of these same 

 dorso-lateral surfaces form a part of the ventral wall of the 

 trachea. The base, or basal surface, lies in the same plane as 

 the corresponding surface of the shaft of the pessulus, and like 

 the latter surface can be plainly seen in a \'iew of the caudal 

 aspect of the entire syrinx. 



The dorsal extremity of the pessulus, like the ventral, is a three- 

 sided pyramid with its apex pointing cephalad. A ventral 

 border and two lateral borders, a dor.sal surface and two ventro- 

 lateral surfaces, and a base, or basal surface, are to be noted. 

 With the exception of the dorsal surface, the surfaces and borders 

 of this extremity have the same corresponding relations as those 

 of the ventral extremity. The dorsal surface lies in close rela- 

 tion to the ventral wall of the oesophagus. To no part of this 

 extremity, however, do the intermediate syringeal cartilages find 

 attachment. 



The first bronchial half -ring is attached at both ends to the 

 lateral borders of the extremities of the pessulus. At its dorsal 

 end this connection is composed of fibrous connective tissue. 

 At the ventral end the union is made by means of cartilage. 

 In old age, however, these attachments become ossified. In 

 females of one or two years the half-rings are united to the ven- 

 tral extremity of the pessulus by young cartilage which appears 

 much lighter than other cartilaginous portions, when stained 

 with hematoxyhn. 



The four cartilages w^hich . occur between the tympanum 

 and the first bronchial half-rings (fig. 4), and which have been 

 designated above as the intermediate syringeal cartilages, appear 

 to differ structurally from all the other cartilages in the entire 

 respirator}^ tract. They are not complete rings nor are they half- 

 rings. Ventrally they are continuous with the pjTamid of the 

 pessulus, while dorsally they are free. The most cephahc ones 

 are smallest and the most rudimentary. Ventrally they pro- 

 ceed from the very apex of the pyramid of the pessulus, extend 

 along the sides of the syrinx as thin flat bands, and end before 



