DIRECTIONS FOR MEASUREMENT. 55 
species of the genus. We have a reference to several standard authors, 
which may be consulted if desired. Turning back a few pages, we find that 
the genus Picus belongs to the sub-family Picine, of the family Picide, of 
the order Scansores; and each of these groups is defined, illustrated, or 
otherwise noticed. In this way, it is believed, a single specimen may 
be made the means of imparting no inconsiderable amount of information. 
2. HOW TO MEASURE A SPECIMEN. 
§ 95. For large birds, a tape line showing inches and fourths will do: 
for small ones, a foot rule, graduated for inches and eighths, or better, deci- 
mals to hundredths, must be used ; and for all nice measurements the divid- 
ers are indispensable. 
§ 96. Ivy comparing measurements made with those given in the Synop- 
sis, absolute agreement must not be expected; individual specimens vary 
too much for this. It will generally be satisfactory enough, if the discrep- 
ancy is not beyond certain bounds. A variation of, say, five per cent., may 
be safely allowed on birds not larger than a robin: from this size up to that 
of a crow or hawk, ten per cent.; for larger birds even more. Some birds 
vary up to twenty or twenty-five per cent., in their total length at least. 
So if I say of a sparrow for instance, “length five inches,” and the speci- 
men is found to be anywhere between four and three-fourths and five and 
one-fourth, it will be quite near enough. ut:—the relative proportions 
of the different parts of a bird are much more constant, and here less dis- 
crepancy is allowable. Thus “tarsus longer than the middle toe,” or the re- 
verse, is often a matter of much less than a quarter of an inch: and as it is 
upon just such nice points as this that a great many of the generic analyses 
rest, the necessity of the utmost accuracy in measuring, for use of the key, 
becomes obvious. When I find it necessary to use the qualification “about” 
(as, “bill abowt—tarsus”) I probably never mean to indicate a difference of 
more than five per cent. of the length of the part in question. 
§ 97. “Leneru.” Distance between the tip of the bill and the end of the 
longest tail feather. Lay the bird on its back on the ruler on a table, take 
hold of the bill with one hand, and of both legs with the other; pull with 
reasonable force, to get the curve all out of the neck; hold the bird thus 
with tip of the bill flush with the end of the rule, and see how much the end 
of the tail points to. Put the tape line in place of the ruler, in the same 
way, for larger birds. 
§ 98. “Exrenr.” Distance between the tips of the outspread wings. 
They must be fully outstretched. With the bird on its back, crosswise on 
the ruler, its bill pointing to your breast, take hold of right and left meta- 
carpus with thumb and forefinger of your right and left hand, respectively, 
stretch with reasonable force, getting one wing-tip flush with one end of the 
ruler, and see how much the other wing-tip points to. With large birds, 
pull away as hard as you please, and use the table, floor, or side of the 
room, as convenient ; mark the points and apply tape line. 
