THE SYRINX OF GALLUS DOMESTICUS 177 



line cartilage throughout; the third and the fourth are entirely of 

 bone. The remaining rings of the trachea are also bone, but 

 each is separated from the next by a small space, which is bridged 

 by a heavy band of fibrous tissiie which, on reaching the rings, 

 becomes continuous with their periosteum. 



The first and the second intermediate syringeal cartilages are 

 small, thin, cartilaginous bars, each having a very thin and in- 

 dist'nct perichondrium. These cartilages are very rudimentary 

 in every respect. The and the third fourthin termediate carti- 

 lages are much better developed and possess well marked 

 perichondria. 



Each intercartilaginous space, from the caudal border of the 

 tympanum to the cephalic border of the fourth intermediate 

 cartilage, is occupied by a strong thick band of fibrous tissue. 

 As determined, after staining with Weigert's elastic tissue stain, 

 these bands are composed almost entirely of elastic fibers. 



As seen in figure 5, the fii'st and the second bronchial half- 

 rings are cartilaginous, but as pre\dously mentioned, the ventral 

 extremity of the first becomes ossified in old individuals. 



The pessulus appears triangular in cross section, and is ossi- 

 fied throughout its entire extent. The marrow cavity is usually 

 quite extensive, and is surrounded by a comparatively thin layer 

 of compact bone. The lateral surfaces of the pessulus, as well 

 as its cephalic and lateral borders, are covered by the mucous 

 membrane of the respiratory tract. A distinct areolar tunic, or 

 submucosa, especially marked over the cephalic border, connects 

 the respiratory membrane to the periosteum of the pessulus. A 

 somewhat different arrangement is found on the caudal surface 

 of the pessulus. ^ Here an areolar coat, continuous with the 

 bronchial submucosa, connects the periosteum of the pessulus 

 with the membranous reduplications in the interbronchial inter- 

 val iinmediately cephalad to the bronchidesmus. 



Above the tj^mpanum the epithelium of the tracheal mucous 

 membrane is of the stratified ciliated columnar varietj^, with a 

 distinct basement membrane. The tunica propria is well de- 

 veloped and contains many lymph cells as well as numerous dis- 

 tinct lymph nodules. These nodules, which are most numerous 



