218 MARSHALL— A STUDY OF THE [June i y , 



One pair comes off on each side from the last tracheal ring, and 

 continues anteriorly almost to the larynx, at which point it spreads 

 out fan-like, the delicate fibers being attached to the upper end of 

 the windpipe ; this muscle is the trachealis lateralis (Tr. Lai.), 

 named according to the description given by Shufeldt (1890), 1 

 though it does not agree in all points with it; there is a partial 

 agreement with Gadow's (/. c. ) m. tracheo-bronchialis. The sec- 

 ond pair of muscles is much stronger but shorter than the last 

 described, and the origin is more ventral. They arise from the 

 trachea on each side between the sixth and the tenth rings, count- 

 ing forward from the last tracheal ring. The muscles become grad- 

 ually smaller as they approach the insertion which is about the mid- 

 point of the proximal part of the first rib articulating with the 

 sternum. This is the m. stemo-trachealis {St. tr.), though it does 

 not agree in all points with Gadow's (/. c.) description of the 

 muscle of the same name. 



The syrinx (PI. IV, Figs. 7, 8) is tracheo-bronchial. On the 

 ventral surface (Fig. 7) the last tracheal ring is directed downward 

 forming with the one above an almost triangular space, of which 

 the preceding tracheal ring is the base. Corresponding to the last 

 tracheal ring on the left side there are two on the right, separated 

 by a small space. These rings and the first bronchial rings are 

 fused at their inner extremities to a small membrane at the base 

 of which the bronchii separate. This membrane is stronger than 

 that between the rings, and is of a yellowish color. The second 

 bronchial ring bifurcates at its inner extremity, the lower branch 

 fusing with the following ring, thus causing it to be much enlarged 

 at its inner termination. Each bronchus is bounded on its inner 

 surface by a cartilaginous rod, and this rod closes the almost circular 

 space embraced partially by the above mentioned bifurcation. The 

 second, third and fourth rings are larger than any of the others, less 

 flexible, and of a yellowish color. 



The membrana tympaniformis externa (Tvm. ex.), is double in 

 this bird. It is bounded by the second and fourth rings, and 

 crossed in the middle by the third. This third ring is larger than 

 the other two. The fourth at its inner extremity loses the yellow- 

 ish color and for this reason seems shorter than it really is. In all, 

 the number of rings in the right bronchus is fourteen and in the 

 left twelve. This may be an individual variation. 



1 Myology of the Raven, Philadelphia, 1S90. 



