102 COMMON TERN. 



ish; the feet orange-yellow. The colours are as in the adult, the forehead 

 white, the rest of the head dusky, the upper parts having the feathers slightly 

 margined with lighter. 



Length to end of tail 12f, to the fork 11; to end of wings 14, to end of 

 claws 10|-; extent of wings 29i; wing from flexure 8f. 



American and British specimens present no essential differences when 

 compared in considerable numbers. The outer web of the lateral tail-feather 

 is blackish-grey, and the inner webs of the tail-feathers are white in all the 

 specimens collected for comparison. The tarsus in American specimens 

 varies in length from 9 to 10^ twelfths, and the claw of the middle toe from 

 2\ to A\ twelfths; but similar differences are observed in the British birds. 



The tongue is 1 T 4 2 inches long, sagittate and papillate at the base, very 

 slender, tapering, the point slit, the upper surface a little concave, the lower 

 horny towards the end. Aperture of posterior nares linear, 9 twelfths long. 

 Palate with a middle and two lateral ridges. (Esophagus 6 inches long, 

 extremely wide, its average diameter on the neck 7 twelfths, within the 

 thorax 11 twelfths. The stomach is muscular, 1 inch long, the lateral mus- 

 cles not distinguishable, the fasciculi of fibres being disposed as in the rapa- 

 cious birds; the central tendinous spaces 3 twelfths in diameter; the cuticular 

 lining strong, with broad longitudinal rugce. The contents of the stomach, 

 fishes. The proventriculus 1 inch long. Intestine 1 foot 7 inches long, of 

 moderate diameter, convoluted, varying from 2\ twelfths to Z\ twelfths. 

 Rectum 1 inch long. Cceca 5 twelfths long, with a diameter of f of a 

 twelfth. 



The trachea is 3$ inches long, 2\ twelfths in breadth above, 1^ twelfths 

 below; its rings 103, feeble and unossified; the lateral muscles extremely 

 slender; there are sterno-tracheal muscles, but none besides. Bronchial half- 

 rings about 18. 



