RET. W. HINCKS ON CT&NUS PASSMORI. 7 



Fig. 6. Sternum of Cygnus hucdnator, laid on its side ; a portion of the bone 

 of the hollow carina being removed, to show the course of the trachea. 

 a. The trachea entering the carina. 



h. The same, just reaching the place where it rises into the projec- 

 tion at the posterior part of the sternum. 

 c. The trachea retm-ning from the wide bow formed at the pos- 

 terior part of the sternum, and bending upwards to enter 

 the tumoiur after a flexure, within which it proceeds outward 

 and upwards in the usual manner. 

 Fig. 7. Inner surface of the sternum of Cygnus buccinator, reduced to the pro- 

 portion of three to five, showing 

 a. The cordiform enlargement, formed by a horizontal flexure of 

 the trachea, and raised half an inch from the general level 

 of the sternum. 

 h. The tumom' at the anterior extremity of the sternum, rising two 

 inches above the level, and one inch above the vertical bone, 

 which the tumour in C Passmori only equals in height. 

 e. The course of the trachea manifested externally, but without any 

 elevation, the part about c being on the level of the surface 

 of the sternum. 

 The figure represents the sternum lying on its side, with the inner 

 surface to the observer, the light coming from the posterior end. 

 Fig. 8. Upper portion of the trachea, with the bone of divarication, showing 

 the broad rings and the mode in which they meet one another. 



[Read May 5, 1864.] 



Note. — The following is extracted from a letter received from 

 Mr. Hincks since his paper was read : — 



" Toronto, April 10th, 1864. 

 " During this winter I have made great efforts to obtain 

 specimens throwing light upon the character of my supposed 

 new species ; and though the season has not been very favourable 

 for bringing Swans our way, I have succeeded in obtaining two 

 young male Swans with the entirely black beak of Cygnus bucci- 

 nator, whose sternum I have carefully examined. I take them 

 both to be younger birds than those previously in my possession ; 

 and I am in doubt whether, beginning with the younger, and 

 placing our C. Passmori as part of the series, we have not a suc- 

 cession of degrees of development according to age, leadiag up to 

 the condition of the trachea in what I have sent as the true 

 G. buccinator. This supposition assumes that the trachea extends 

 with age, that it enters the hollow carina of the sternum, and 

 soon shows a tendency to a double bend; that the pressure of the 

 trachea on the bone of the sternum would modify its (the boners) 

 shape (as physiologists will readily acknowledge it might do), and 



