158 ESSENTIALS OF ZOOLOGY 



trally located hem^t which is divided into chambers. The blood con- 

 tains hemoglobin-hearing red corpuscles and amoeboid white corpus- 

 cles. In the vertebrate body is a well-developed coelom, which encloses 

 advanced systems of organs for digestion, excretion, circulation, 

 reproduction, and, in terrestrial forms, respiration. C ephalization is 

 developed in all vertebrates and along with this they possess a 

 hollow, five-lobed brain located in the more or less distinct head. 

 The sense organs are in an advanced state of development. The body 

 is divided into head, trunk, and tail. The tail is a posterior pro- 

 longation of the body behind the anal opening and is found in some 

 degree in all vertebrates. The neck which is a constricted region 

 between trunk and head is conspicuous in terrestrial forms. The 

 appendages are usually arranged with one pair attached to the ante- 

 rior, pectoral portion of the trunk and one situated at the posterior, 

 pelvic region. This arrangement is less consistent in the aquatic 

 types where the weight of the body is buoyed up by the water and 

 the limbs are used less for support and locomotion. In different 

 types of vertebrates there are various modifications of pectoral ap- 

 pendages as arms, wings, pectoral fins, forelegs, and flippers. The 

 same is generally true for the pelvic limbs. 



The vertebrate animal is covered by an integument or shin which 

 serves as a protective and sensory organ. It also helps in excretion 

 through the sweat glojids, mucus glands, and oil glands as well as 

 facilitating temperature regulation in some. Such exoskeletal struc- 

 tures as scales, nails, hoofs, claws, feathers, hairs and enamel of teeth 

 are produced by the skin. 



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. The exo- 

 skeleton is a rather minor part in vertebrates and consists of nails, 

 claws, scales, hair, feathers, and other outgrowths. The endoskele- 

 ton includes the axial and appendicular portions. The first is com- 

 posed 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. The vertebral column is composed 

 of segmental divisions, the vertebrae, and is divided into five regions 

 as follows : cervical vertebrae of the neck, thoracic vertebrae 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. 



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