1885.] 



DR. H. GADOW ON THK SPECIES OF RHEA. 



319 



The number of tracheal rings in Rh. macrorhyncha is 1 85, in 

 Rh. dai-wini 152 ; and the rings themselves are comparatively broader 

 and thicker in the latter species, thus making up for their con- 

 siderably smaller number, as the length of the whole trachea does 

 not show any important differences in the two species. The syrino-eal 

 muscle described by Forbes exists in all the specimens dissected by 

 me; however, in level of the 9-1 1th last tracheal rings, the upper 

 end of the tracheo-bronchial muscle passes into the lower end of the 



Fis. 9. 



Fig. 10. 



Rh. macrorhyncha. Rh. darwini. 



Dorsal vievr of tongue, larynx, and syrinx. N, branch of hypoglossal nerve. 



long m. cerato-trachealis, which runs down from the cerato-hyal 

 along the side of the trachea. Both these muscles and the m. tracheo- 

 sternalis are supplied by branches of the descending ramus of the 

 hypoglossal nerve, thus leaving no doubt as to their common origin 

 from muscles of the hyoid arches. 



In all other respects the syrinx of my specimens of Rhea darwini 

 and R. macrorhyncha agrees with the description given by Forbes. 

 The slight modifications concerning the partial fusion of the last 

 tracheal rings are easily explained by differences of age and indi- 

 vidual variation. The same, I am sorry to say, applies to the vas- 

 cular and genital systems. 



