THE SYRINX OF GALLUS DOMESTICUS 187 



intermediate cartilages are here represented by extremely small 

 masses which lack the regular cell arrangement found in the 

 others. Ventrally they fuse with the ventral pyramid of the 

 pessulus. Immediately caudad to the first half-rings is a mesen- 

 chymal area, which is apparently condensing to form the anlage 

 for the second half-ring. None of the other bronchial cartilages 

 are represented at this stage. 



At 260 hours the central cells of the anlagen for the first half- 

 rings, the fourth intermediate syringeal cartilages, and the pessu- 

 lus appear slightly more separated from each other. As would 

 be expected from the order of their fu'st appearance this is most 

 marked in the anlagen for the first half-rings, where true embry- 

 onal cartilage is closely approached, and least marked in the 

 pessulus. The first seven half-rings are represented at this stage. 



All the cartilaginous and the bony skeletal elements of the res- 

 piratory tract are represented in an embryo of 284 hours. The 

 pessulus, the first and the second half-rings, the tracheal rings 

 (except the fu'st and the second) and the fourth intermediate 

 syringeal cartilages are composed of embryonal or primary car- 

 tilage. The perichondrium is represented by a thin layer of 

 cells which are very much elongated and rather sparsely distrib- 

 uted. All skeletal elements, other than those above mentioned, 

 are still in the mesenchymal stage. Figure 10, drawn from a 

 wax reconstruction of the syrinx of a 284 hour chick, shows the 

 extent, the size, the form, etc., of the cartilages, and their rela- 

 tion to the epithelial tube. All the intermediate syi'ingeal car- 

 tilages are fused to the ventral pyramid of the pessulus. The 

 fourth are much the largest of these and closely approach the 

 first half-rings in size. They present a decided cephalic arching 

 in the middle portion of their course, and each shows a marked 

 enlargement, which ends freely, but in close relation to the middle 

 third of the dorsal pyramid of the pessulus. The third, with 

 a diameter about one-half as great as that of the fourth, and 

 placed slightly cephalad to the latter, pass around the epithelial 

 tube and present free dorsal extremities, which he cephalad and 

 lateral to the apex of the dorsal pyramid of the pessulus. The 

 second are much smaller and take a course parallel to that of the 



