Mr. SELBYon a new Spepies of Swan. 23 



the Hooper it rarely exceeds four inches in depth, and never reaches the 

 extremity of the keel, or occupies any portion of the lateral part of the 

 sternum. In birds of a younger age, or which have not acquired the 

 full developement of the tracheal tube, the loop, or horizontal bend, is 

 much less, and does not occupy the whole of the orbicular portion of 

 the cavity prepared for it, as shewn in PL V. fig. 2 ; and in still younger 

 birds the trachea is seen to enter only a short way within the excavation 

 of the keel, and then to make a vertical deflection, as in PI. VII. fig. 3, 

 although the cavity in that part of the sternum destined to receive the 

 horizontal bend already exists and is partially excavated. In the new spe- 

 cies, the keel does not project so far as in the Hooper, in consequence 

 of which, the perpendicular depth of the cavity in that of the former is 

 not so great, and the entering and returning portions of the trachea more 

 compressed, or brought closer together, than the corresponding parts of 

 the latter ; the ridge of the keel in the two species is also different ; in 

 the Hooper narrowing from above downwards ; in the new species, on the 

 contrary, it becomes broader as it descends towards the extremity, where 

 it is found considerably expanded, as in PI. VI. figs. 3 & 4. The lateral por- 

 tion of the sternum is also much wider in comparison to the size of the 

 bird in the new species, than in the Hooper, and its general form and pro- 

 portions appear very different when placed along side of each other. 

 Tracing the trachea of the new species, after its egress from the hollow 

 cavity of the keel, and the bend it makes on its approach to the thorax, 

 a very marked difference becomes apparent at its lower portion, or where 

 it is joined to the inferior larynx, or bone of divarication, to which are 

 attached the bronchial tubes, as compared with the same parts in the 

 Hooper. In the new species, the trachea itself, after describing the arch, 

 enters a considerable way within the cavity of the thorax, as shewn in 

 PI. V. figs. 1 & 3, where it is joined to the inferior larynx or bone of diva- 

 rication ; at this part it swells considerably in volume, and its diameter, 

 where it joins the larynx, is greater than at any other part of the trachea ; 

 the bone of divarication is also of considerable width (PI. VI. fig. 5), its 

 transverse diameter being more than double that of the Hooper, and its 

 position within the thorax is vertical, as shewn in PL V. figs. 1 & 3. In 



