294 ANATOMY AND PHYSIOLOGY OF THE FOWL 
are exceptions). The toes end in claws which aid in scratching 
and perching. The four toes are arranged with three in front and 
one behind, except in the five-toed breeds, which have two behind. 
The spur above the toes is most developed in males as a means 
of defence. 
The sternum, or breast bone, is one of the most highly developed 
bones in the fowl’s skeleton. It is very large and projects far back 
beyond the ribs, forming a large part of the abdominal wall. It 
is so situated as to protect the vital organs lying above it. There 
is a thin blade called the keel, which forms an attachment for the. 
flight muscles, and its size varies greatly as the sizes of the wings 
vary. Some breeds with small wings have no incentive to flight. 
They have small keels and a correspondingly small amount of 
breast meat. 
The two clavicles, commonly called in the human skeleton the 
collar bones, are thin bones, the lower points being attached and 
the upper slightly spread, thus forming a spring which aids in 
working the wings. The united clavicles are often called the ‘ wish 
bone.” 
The fowl’s head is small in comparison with other body parts, 
and is characterized by lightness and the fusion of cranial bones. 
The jaws are commonly called mandibles and form the bird’s beak. 
Just back of the upper mandible are the nasal cavities, which are 
relatively small and open by means of small slits into the interior 
of the mouth. These slits are found open when the bird’s head is 
down, and closed when the head is elevated; hence the necessity 
for the bird to raise its head when drinking, to keep the water 
from running out of the nostrils. 
The vertebral column of the fowl is characterized by the great 
length of the neck, by its mobility, and by the rigidity of the back, 
loin, and tail. 
The pelvic arch is composed of the ilium and acetabulum above 
and the ischium coming down each side, forming what are com- 
monly called the “lay bones” in the hen. These four bones 
assume various positions at different stages of the laying period. 
The Physiological Organization of the Fowl.—It is well to 
understand the elementary parts of the animal structure and their 
relation to one another. These are the cells, various kinds of 
tissues, organs, and their resulting system. 
A cell is the most elementary living part of the body. There 
are millions of these, of various shapes, according to the tissues 
