92 
GENERAL OBNITHOLOGY. 
accomplish their office by running through pulleys to change the line of their traction. They 
work like men hoisting sails from the deck of a vessel ; and thus, like a ship's cargo, a bird's 
chief weight is kept below the centre of motion. Top-heaviness is further obviated by the way 
in which birds with a long heavy neck and head draw these parts in upon the breast, and 
extend the legs behind, as is well shown by the attitude of a heron flying. The nice adjust- 
ment of balance by the variable extension of the head and feet is exactly like that produced in 
weighing by shifting a weight along the arm of a steel-yard ; and together with the slinging 
of the chief weight under the wings instead of over or even between them, enables a bird to 
easily keep right side up in flight. The 
Exterior of a Bird is divided for purposes of description into seven parts : — 1. The head 
(Lat. caput) ; 2. The neck (Lat. collum) ; 3. The body proper, or trunk (Lat. truncus) ; 4. 
The bill or beak (Lat. rostrum) ; 5. The wings (Lat. pi. alee) ; 6. The tail (Lat. caudd) ; 7- 
The feet (Lat. pi. pedes). Of these, 1, 2, 3, the head, neck, and trunk, are collectively termed 
the hody (Lat. corpus), in distinction from 4, 5, 6, 7, which are the members (Lat. membra). 
The wings and feet are of course double or paired parts. The bill is strictly but a part of the 
head ; but its manifold uses as an organ of prehension make it functionally a hand, and there- 
fore one of the members." The 
Head has the general shape of a four-sided pyramid ; of which the base is applied to the 
end of the neck, therefore not appearing from the exterior, and the apex of which is frustrated 
at the base of the bill. The uppermost side is more or less convex or vaulted, sloping in 
every direction ; the under side is flattish and horizontal ; the lateral surfaces are flattish and 
vertical ; aU similarly taper forward. The departures from any such typical shape are endless 
in degree and variable in kind, giving rise to numerous general descriptive terms, such as 
'^head flattened," "head globular," but not susceptible of exact definition. The head is 
moulded, of course, upon the skull, corresponding in a general way to the brain-cavity of the 
cranium proper, both in size and shape ; but it differs in several particulars. In the first place, 
there is the scaffolding of the jaws; seccmdly, large excavations to receive the eye-balls, and 
smaller ones for the ear-parts ; thirdly, muscular masses overlying the bone ; and lastly, in 
some birds, large hollow spaces in the bone between the inner and outer tables or plates of the 
cranial walls. Each side of the head presents two openings for the eye (Lat. oculus) and ear 
(Lat. auris), the position of which is variable, both absolutely and in relation to each other. 
But in the vast majority of birds, the eye is strictly lateral in situation, and near the middle of 
the side of the head ; while the ear is behind and a little below the eye, near the articulation 
of the lower jaw. Bnt the shape of the skull of owls is such, that the eyes are directed forward, 
and such birds are said to have eyes anterior." Owls also have enormous outer ears, in some 
cases provided with a movable flap or conch, closing upon the opening like the lid of a box ; 
and in many cases their ear-parts, and some of the cranium itself, is unsymmetrical. In 
most birds the ear-opening is quite small, and only covered by modified feathers. In the 
woodcock and snipe, owing to the way the brain-box is tilted up, the ears are below and not 
behind the eyes. The month (Lat. os, gen. oris) is always a fissure across the front of the head. 
The cleavage varies, both in extent and direction ; the latter is usually horizontal, or nearly 
so, but may trend much downward ; the former varies from a mininum, in which the cleft does 
not reach back of the horny part of the bill, as in a snipe, to the maximum seen in fissure-billed 
birds like the swifts and goatsuckers, which gape almost from ear to ear. There are no other 
openings iu the head proper, for the nostrils are always in the bill. The 
Neck, in effect, is a simple cylinder, rendered somewhat hour-glass-shaped, as above said. 
It consists of a movable chain of bones, the cervical vertebrce (Lat. cervix, the neck ; verto, I 
