THE SYRINX OF GALLUS DOMESTICUS 201 



taken the shape of those found in the adult. No bone is present 

 at the time of hatching. 



6. CiUated cells are present in stages beyond 248 hours but 

 were not observed in the region of the future tympanic 

 membranes. 



7. Mucous cells were first observed in 332 hour embryos and 

 only in later stages were they found arranged in the form of sim- 

 ple alveolar glands. 



8. Muscular tissue is differentiated in the 176 hour stage. 

 Muscle fibers showing faint cross striations appear at 296 hours. 

 At 452 hours the muscles are well developed. 



9. At the time of hatching the tympanic membranes are thick. 

 They are covered, however, as in the adult, with a single layer 

 of epithehal cells. 



FUNCTION. 



1. That the syiinx is the true voice organ of the chicken is 

 evident from the following deductions : 



First, structurally it is the only part of the respiratory tract 

 capable of producing sound. 



Second, when the trachea is divided and the cephalic portion 

 tightly tied, the chicken is still able to crow. 



Third, after di\dsion of the trachea, voice can be reproduced 

 artificially by forcing air into the air sacs. 



2. The upper larynx serves only to modulate the voice. 



3. The sterno-tracheal muscles, by their contraction, shorten 

 the trachea and modify pitch. They also draw the tympanum 

 cephalad, thus indirectly varying the tenseness of the tympanic 

 membranes. 



4. The air sacs are necessary in voice production, for voice 

 could not be produced artificially after puncturing the cervical 



JOURNAL OF MORPHOLOGY, VOL. 



