THE SYRINX OF GALLUS DOMESTICUS 169 



stain. These organs were then washed and cleared, after which 

 the cartilaginous and the bony structures could be more easily 

 studied with the binocular microscope. Owing, however, to the 

 size and the shape of the organ as a whole, this method was not 

 entirety satisfactory. Third, wax reconstructions were made 

 according to the method described by Born. 



The syringeal skeleton (fig. 4) consists of (1) the first four 

 tracheal rings which may be designated, the cephahc sjTingeal 

 skeletal elements; (2) the first three bronchial half-rings, or the 

 caudal syringeal skeletal elements; (3) four modified cartilages, 

 neither rings nor half-rings, which are found between the tra- 

 cheal rings and the first bronchial half-rings. These modified 

 structures will be designated the intermediate syringeal , car- 

 tilages; (4) a bony pessulus which hes at the summit of the 

 bronchial junction in the dorso-ventral plane and transverse 

 to the long axis of the trachea. Although the skeletal elements 

 are similar in most respects in both sexes, the following de- 

 scription apphes, unless stated otherwise, only to the male. 



The typical tracheal rings are broad flat bands of cartilage. 

 They differ from the type found in most of the higher animals 

 in that they are complete rings. In cross section the typical 

 rings have a cephalo-caudal diameter which is much greater 

 than the medio-lateral diameter, hence they appear very much 

 elongated (fig. 5). But as the caudal end of the trachea is ap- 

 proached, the cephalo-caudal diameter of the rings diminishes 

 while the medio-lateral diameter increases. The fifth, the sixth, 

 and the seventh rings appear almost square when seen in cross 

 section. These, as well as all other rings cephalad of them, 

 are transverse to the long axis of the trachea and constitute the 

 framework of its walls. The medio-lateral diameter of the fourth 

 ring is greater than its cephalo-caudal diameter. The most 

 ventral portion of this cartilage dips caudad to a considerable 

 extent. 



The first four tracheal rings (fig. 4) are very closely related to 

 each other. They are partially fused along their sides as well as 

 firmly bound together by dense fibrous tissue. Their ventral 

 and dorsal extremities are free, but the spaces between these 



