A History 
of Birds. 
(16) 
THE BIRD WORLD. 
A History of Birds. 
By W. P- PYECRAFT, A.L.S., F.Z.S., etc, 
(Continued from p. 154, Vol. I.) 
CHAPTER IV. 
THE ORGANS OF DIGESTION. 
Though once upon a time birds were 
burdened with teeth, they long ago 
solved the problem of doing without 
them, and thereby they are to be envied. 
Like the Tortoise and Turtle among the 
reptiles, birds have replaced their teeth 
by horny sheaths which encase the jaws; 
and these sheaths take many forms. As 
a rule, that of the upper differs but little 
from that of the under jaw, but in many 
birds this is not so. In the birds of 
prey, for example, which tear their food 
in pieces, the sheath of the upper jaw is 
hook-shaped; and this is true also of the 
Parrots. The latter, as most of my 
readers are probably aware, have the 
under surface of the hook of the upper 
jaw curiously ridged, forming what is 
known as the “ file,” whose purpose, so 
far, appears to be a matter for specula¬ 
tion. Birds which seize rapidly-moving 
prey, such as fish, have spear-shaped 
beaks, such as Herons and Kingfishers; 
and a similar weapon is developed where 
a rapid succession of blows is rained 
upon hard and unyielding substances, as 
in the beaks of Woodpeckers, which, 
moreover, have the density of the horn 
enormously increased. On the other 
hand, these sheaths are often of great 
delicacy, as in the case of Snipe and 
Woodcock, the fragile, upturned beak of 
the Avocet, or the long rod-like prolan 
of many Humming Birds. 
The Beaks Fashioned'to Food . 
In the so-called soft-billed birds, the 
jaws seem merely as light forceps, and, 
consequently, they and their sheaths offer 
no very striking characters; while in 
birds like Swallows, Swifts, and Night¬ 
jars the beak has degenerated to the 
smallest possible limits, and this because 
the jaws are hardly used in the capture 
of prey. Where slippery victims have 
to be held, the edges of these horny 
sheaths develop more or fewer saw-like 
teeth, as in Mergansers, or these teeth 
may take the form of needle-like spines, 
as in the Darters. In the Ducks, and 
certain Petrels, horny plates, really the 
baleen-plates of “ whalebone ” whales, 
are developed, and these serve as 
sieves, or strainers, allowing the water 
taken in by the mouth free exit, but 
retaining the minute living organisms 
which serve these birds as food. In the 
Shirella Ducks these plates attain their 
highest development. 
Those portions of the jaws which are 
thus encased in horn form the “ beak ” 
of birds, and the shape of this again is 
determined by the nature of the food it 
is required to manipulate. That the 
beak forms, then, an important part of 
the alimentary canal is a fact which, 
perhaps, we do not often realise; but 
the beak is the fore-part of the mouth, 
and no one will deny that the mouth is a 
very important agent indeed in supplying 
the needs of the body. 
The Bur pose of the Crop. 
From the mouth the food is passed 
down the gullet, or oesophagus, until, in 
many birds, such as Pigeons and Fowls, 
it reaches a special dilatation of the 
gullet known as the “crop.” This is a 
thin-walled bag, wherein the food, is 
stored and softened, preparatory to being 
passed on to the stomach. This, in 
birds, consists of two parts, one lying 
in front of the other. The first, which 
superficially is hardly distinguishable 
from the gullet, is known as the “ proven- 
triculus.” The walls thereof develop 
special digestive glands, which are gener¬ 
ally grouped together to form patches 
varying in area and in shape. From 
this first stomach the food passes on to 
the second, which in birds, such as 
Fowls and Pigeons, for example, has ex¬ 
ceedingly thick muscular walls, while its 
cavity is lim'd by a more or less dense 
