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DIRECTIONS FOR MEASUREMENT. 57 
birds, there is a slight elevated point right in the middle; this, or the posi- 
tion of it in other birds, is the precise place. Place the other foot of the 
dividers over the transverse line of jointing of the base of the middle toe. 
This latter point, in all birds, when the toes are bent backward, becomes a 
more or less salient angle easily determined. In hard-legged birds it is 
usually indicated by the termination of last tarsal scutellum ; in water birds, 
there will be seen a little crosswise nick, showing just where the skin has 
shrunk into the crack between the end of the metatarsus and the base of 
the toe. It will be evident that a measurement taken as here directed will 
not always be the same as one taken behind, up over the convexity of the 
heel, and down to the level of the sole; but there are behind no other 
tangible points of termination. (See fig. 9, és.) What, now, is the mean- 
ing of the expression —“d. = $ trs.”? 
§ 103. “Leneru or tors.” Distance in a straight line along the upper 
surface of a toe, from the point last indicated, to the root of the claw on 
top. Observe that, as the claws are inserted upon the ends of the toes, 
somewhat as the nails are on our fingers, this measurement is a different 
thing from one taken along the under surface of the toes. Always make 
it with the dividers. Length of toe is always taken without the claw unless 
otherwise specified. When no particular toe is specified, 3¢ is always 
meant. (See fig. 9, 3écl.) Define this expression : —“érs.> 3¢.” 
. § 104. “Lenera or tHe ciaws.” Distance in a straight line from the 
point last indicated to the tip of the claw. (See § 101.) When this 
measurement is meant to be included in the length of toe, I say écl. 
Determine this : —“‘érs. < 3¢cl.” 
§ 105. “Leneru of HEAD” is an often convenient dimension for compar- 
ison with the bill. Set one foot of the dividers on the base of culmen 
(determined as above), and allow the other to just slip snugly down over 
the arch of the occiput. This is the required measurement. What does 
this mean :—“/d. = b.”? 
§ 106. ALL MrasuREMENTS are in the English inch and vulgar fractions 
or decimals, unless otherwise specified. 
§ 107. Fryatty, it may be well to call attention to the fact, that most 
persons unaccustomed to handling birds are liable to be deceived in attempt- 
ing to estimate a given dimension; they generally make it out less than 
measurement shows it to be. This seems to be an optical effect connected 
with the solidarity of the object, as is well illustrated in drawing plates of 
birds, which, when made exactly of life-size, always look larger than the 
original, on account of the flatness of the paper. The ruler or tape-line, 
therefore, should always be used, and are more particularly necessary in 
those cases where analyses in the Key rest upon dimensions. It is hardly 
necessary to add, that in taking, approximately, the total length from a 
prepared specimen, regard should be had for the “make-up” of the skin. A 
little practice will enable one to determine pretty accurately how much a 
skin is stretched or shrunken, and to make the due allowance in either case. 
KEY TO N. A. BIRDS. 8 
