MEASUREMENTS. 
LENGTH. — Distance in a straight line from the end of the bill to the tip 
of the longest tail feather. Occasionally the middle feathers are much 
elongated, as in Phaethon and Stercorarius. 
WING. — Distance from the carpal joint (bend of the wing) to the tip of 
the longest primary. 
TAIL. — Distance from the tip of the longest tail feather to its base (the 
point where it enters the body). 
BILL. — The distance in a straight line from where the bill (upper mandible) 
joins the skin of the forehead (A) to the tip (B). (There are a few ex- 
ceptions to this rule, such as birds with frontal plate, etc. Some curved 
bills are measured along the curve of the cz/men, but in cases of this kind 
it should always be so stated.) 
TARSUS. — Distance in front of the leg from what appears to be the knee 
joint (end of tibia) to the root of the middle toe. 
All measurements are given in inches and fractions of an inch. 
Birds vary so much in size that the length of any one specimen cannot 
be accepted as a standard for others of the same species. The length measure 
is, nevertheless, of value to enable us to form an approximate idea of the size 
of the bird; the length of the wing is much less variable and is an im- 
portant aid to the identification of certain species. 
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