CHARACTERS OF VERTEBRATE ANIMALS. / 



the delicate vibrations of that atmosphere which follow the mutual 

 contact or percussion of sonorous bodies, and the finer vibrations of 

 a more subtle a3ther, the appreciation of which produces the sense 

 of sight. 



With these means of perceiving, knowing, and investigating the 

 world around them, the Vertebrated animals possess a proportionate 

 power of acting upon and subduing it. Not any species is fixed to 

 the earth ; all can move, and every variety and power of animal 

 locomotion is manifested in the vertebrated sub-kingdom. Yet some 

 permanently retain the worm-like figure, which all primarily manifest 

 in common with the embryos of the articulate series ; but always 

 with the grand difference of the dorsal nervous column. Such 

 vermiform species glide by undulatory inflections of the entire 

 body through the waters, or on the surface of the gi'ound. But in 

 most Vertebrata special instruments of locomotion are developed ; 

 some single from the median line, some in pairs ; the latter never ex- 

 ceed four in number, two before or above, called arras, or pectoral 

 extremities (P), and two below or behind, called legs, or pelvic exti-e- 

 mities ( V) : thus, the vertebrated type is essentially tetrapodal.* The 

 solid mechanical supporting and resisting axis, framework, or lever- 

 age {sk) of these members is internal, vascular, and commonly ossi- 

 fied. It is covered, and, as it were, clothed by the muscles (m), which 

 are attached to its outer surface. The elementary contractile fibre of 

 the voluntary muscular system is transversely striated. 



The internal position of the skeleton seems to be the chief con- 

 dition of the attainment, by certain Vei-tebrata, of a bulk far surpass- 

 ing that of the largest of the Invertebrata : and the division of the 

 skeleton into numerous pieces diversely articulated, gives great variety 

 and precision to the movements of the Vertebrate animals. 



The forms and proportions of the Vertebrata are as varied as their 

 kinds of locomotion, and the elements in which these are exercised. 

 With very few exceptions the body is laterally symmetrical, the right 

 and left sides corresponding. We may likewise discern a general 

 characteristic of the Vertebrata in the tendency to a symmetrical 

 development, or a repetition of parts in the vertical direction ; 

 that is, in the dorsal and ventral regions. Each vertebral segment 

 of the internal skeleton, for example, forms typically a dorsal and a 

 ventral arch ; the one protecting the nervous axis, the other the vas- 

 cular trunks and organs of plastic life. The nervous trunk itself 



* The homologucs of lliesc special instruments of locomotion may exist in 

 j;reater numbers, more or less developed and modified, in subserviency to otlier 

 finictions; as, for example, the opercular and hranchiostegal flaps of fishes, the 

 simple appendages of the ribs in fishes and in l)irds. Tlic arms and legs commence 

 in Lepidosiren, for example, as simple unbranchcd filamentary appendages divergin;' 

 from inferior vertebral aiciies. 



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