80 COMMON TERN. 
claw of the middle toe from 23 to 43 twelfths; but similar differences 
are observed in the British birds. 
The tongue is 1; inch 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. Eso- 
phagus 6 inches long, extremely wide, its average diameter on the 
neck 7 twelfths, within the thorax 11 twelfths. The stomach is mus- 
cular, 1 inch long, the lateral muscles not distinguishable, the fasciculi 
of fibres being disposed as in the rapacious birds; the central tendi- 
nous spaces 3 twelfths in diameter; the cuticular lining strong, with 
broad longitudinal rug. The contents of the stomach, fishes. 'The 
proventriculus 1 inch long. Intestine 1 foot 7 inches long, of mo- 
derate diameter, convoluted, varying from 23 twelfths to 21 twelfths. 
Rectum 1 inch long. Coca 5 twelfths long, with a diameter of } of a 
twelfth. 
The trachea is 31 inches long, 23 twelfths in breadth above, 13 
twelfth below; its rings 103, feeble and unossified; the lateral mus- 
cles extremely slender; there are sterno-tracheal muscles, but none 
besides. Bronchial half-rings about 18. 
