378 TEXTBOOK OF ZOOLOGY 



of the chemical changes and transformations by which energy is 

 supplied for the activities of the protoplasm. 



The skeleton is quite well developed in the vertebrates and serves 

 them quite efficiently for support, stature, protection, and muscle 

 attachment. It is composed of cartilage entirely in some of the 

 simpler forms and of bone and cartilage in higher types. It is divided 

 into an exosJceleton which is superficial and an inner endoskeleton 

 which includes all of the deeper skeletal parts. The exoskeleton is 

 a rather minor part in vertebrates and consists of nails, claws, scales, 

 hair, feathers, and other outgrowths. The endoskeleton includes the 

 axial and appendicular portions. The first is composed of the skull, 

 vertebral column, ribs, and in some a sternum. The appendicular 

 portion is composed of the anterior and posterior girdles and two 

 pairs of limbs. In their development bones either replace cartilage 

 to be called cartilage I ones or they develop in the connective tissue 

 of the dermis, to be known as membrane hones. The vertebral column 

 is composed of segmental divisions, the vertebrae, and is divided into 

 five regions as follows: cervical vertebrae of the neck, thoracic verte- 

 brae of the chest, lumbar vertebrae of the small of the back, sacral, 

 vertebrae of the hip region, and the caudal vertebrae of the tail 

 region. Bone is a firm, hard tissue consisting of abundant matrix, 

 composed of inorganic salts, and the bone cells which are held in 

 pocketlike lacunae in the matrix. The outer membranous covering 

 of bone is called periosteum. The mineral part of the bone consists 

 chiefly of calcium phosphate and calcium carbonate. They give it 

 firmness and rigidity. The animal matter is composed of the bone 

 cells and cartilage which serve to give the bone life and resilience. 

 A weak acid, such as the acetic acid in vinegar, will dissolve the 

 mineral matter of bone if allowed sufficient time, in which case 

 the bone will lose its rigidity. Caustic solutions will destroy the 

 animal matter and make the bone brittle. The following outline 

 presents a summary of the principal parts of the terrestrial verte- 

 brate skeleton. 



Divisions of Skeleton of Terrestrial Vertebrate 



I. Axial Skeleton 

 (a) Skull 



1. Cranium 



2. Sense capsules 



3. Jaw apparatus 

 (Visceral arches) 



