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 



