CHAPTER XXIV 



THE VERTEBRATE ANIMAL: SUBPHYLUM 



VERTEBRATA 



In this group to which man himself belongs are found the dis- 

 tinctive chordate characteristics at some time in the life of the indi- 

 vidual. In terrestrial forms there are certain modifications to pro- 

 duce other structures. Metamerism and bilateral symmetry are 

 universal characteristics among vertebrates. The segmented verte- 

 bral column and other supporting structures form an endoskeleton 

 (internal skeleton) which is the basic support of the body. Paired 

 appendages are usually present at some time in the life of the indi- 

 vidual. The majority have two pairs of fins or limbs in adult con- 

 dition. There is a ventrally located heart which is divided into 

 chambers. The Mood contains hemoglohin hearing red corpuscles and 

 amoeboid white corpuscles. In the vertebrate body is a well-developed 

 coelom, which encloses advanced systems of organs for digestion, ex- 

 cretion, circulation, reproduction, and in terrestrial forms, respiration. 

 Cephalization 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 

 prolongation of the body behind the anal opening and is found in 

 some degree in all vertebrates. The nech 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 

 anterior, 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 appendages as arms, wings, pectoral fins, forelegs, and 

 flippers. The same is generally true for the pelvic limbs. 



The body wall is composed of the skin, which usually has char- 

 acteristic tegumentary outgrowths, such as scales, nails, shells, 

 feathers, and hair, as the outer layer, beneath which is the muscular 



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