INTRODUCTION. 21 
the nape). The “rump” (or lower back) often includes the 
upper tail-coverts, the’ ‘ belly” the undef tail-coverts, etc. 
The “sides” invariably refer to those of the breast and belly. 
§U. Measurements of both birds and eggs are made in 
straight lines between two points. To measure the length of a 
bird, lay it on its back, and make the tip of the bill (so far as 
reasonable), and the end of the longest tail-feather, touch the 
ruler or paper on which they are laid ; then measure the distance 
between these points. Measure (with compasses) the tarsus 
in front, and the bill from the tip of the upper mandible to the 
feathers actually or apparently belonging to the forehead.1 
The “depth” of a bill is its vertical width near the base, when 
closed. Eggs may be measured by dividers, or by a ruler 
. with a slide. For accurate measurements a ruler marked deci- 
mally (or even with hundredths) is best. <4; of an inch equals 
about °06. 
§V. Birds form a class of the Animal Kingdom. They are 
composed of three (or more?) distinct subclasses; the Aves 
Aérece, Insessores, or typical “perchers ;” the Aves Terrestres, 
Cursores, or gallinaceous birds and “‘waders;” and the Aves 
Aquatice, Natatores, or “swimmers.” These are grouped into 
several orders (such as the Raptores or “birds of prey”), 
which are divided into families (as the Raptores into Strigi- 
de, Falconide, etc., or the hawks, including eagles, the owls, 
and vultures). The orders are sometimes more primarily di- 
vided into suborders, and families into subfamilies. Thus the 
Passeres consist of the Oscines or singing passerines, and the 
15 There are other methods of making this measurement, 
