COMMON TERN. 
261 
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 121, to the fork 11 ; to end of wings 14, to end of 
claws 10J ; extent of wings 29i ; wing from flexure 8^. 
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 
21 to 41 twelfths; but similar differences are observed in the British birds. 
The tongue is 1 4 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 ttre rapa- 
cious birds; the central tendinous spaces 3 twelfths in diameter; the cuticular 
lining strong, with broad longitudinal rugae. The contents of the stomach, 
fishes. The proventriculus 1 inch long. Intestine 1 foot 7 inches long, of 
moderate diameter, convoluted, varying from 2f twelfths to 2J twelfths. 
Rectum 1 inch long. Coeca 5 twelfths long, with a diameter of I of a 
twelfth. 
The trachea is 3$ inches long, 2£ twelfths in breadth above, II 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. 
