GREAT NORTHERN DIVER. 



293 





Depth of body, 







— 6 



Breadth, 







Ql 



y 2 



Bill along the ridge, 







q 4 

 °1% 



Gap-line, 







41 



^2 



Tarsus, . 







Q 3_ 



°12 



Hind toe, 







Ql 



y 2 



Its claw, 







2 

 12 



Outer toe and claw, 







41 



Middle toe, 







— 4* 



Inner toe, 







Q_9_ 



°12 



Tail, 







— 29 t l 



Wing from flexure, 







• ~ 14| 



Weight, 







8| 8* 



The female is generally smaller, but in all other respects resembles the 

 male. Weight 10 lbs. 11 oz. 



Young in winter. 



Bill pale yellowish-green, the ridge and tip of the upper mandible dusky. 

 Iris brown. Feet dusky externally, pale yellowish flesh-colour internally, 

 webs dusky, but yellow in the middle. Claws yellowish-brown. All the 

 upper parts are of a uniform dark greyish-brown, each feather margined 

 with lighter, the lower parts white; the sides of the neck at the lower part 

 whitish, streaked with dusky; the sides dusky, without spots. 



Towards spring the eye assumes a redder tint, and the plumage of the 

 upper parts gradually becomes spotted with white; and when the moult is 

 completed about the end of summer, the plumage is as in the adult, although 

 the tints are improved at each successive moult for several years. 



A fine male killed at Boston, 34 inches in length, with an alar extent of 

 56, presents the following characters. There is a general layer of sub- 

 cutaneous adipose tissue, and the skin is very tenacious. The external 

 aperture of the ear roundish, very small, having a diameter of only 2 lines. 

 The tongue is 2 inches 1 line in length, fleshy, as high as broad, slightly 

 concave and longitudinally grooved above, tapering to a horny point. On 

 the palate are 6 rows of papillae; the posterior aperture of the nares is linear, 

 2\ inches in length. The aperture of the glottis is \ an inch long, with 

 numerous papillae along its sides and behind. The pharynx is extremely 

 dilatable, as is the oesophagus, which is 17 inches long, passes along the right 

 side of the neck, together with the trachea, and when distended has an 

 average diameter of 2\ inches, but on entering the thorax contracts to 1^. 

 The structure of the oesophagus in birds may be very conveniently examined 

 in this species, the different layers being remarkably developed in it. 

 Properly speaking, it has only two coats, — the outer muscular, its external 



