154 THE STKUCTUEE OF THE HOESE. 



ages, called " limbs," mainly adapted for the purposes 

 of locomotion, and which are attached to the trunk 

 by the intervention of solid structures, commonly 

 called in anatomical language u girdles." These are 

 so called because the pair of them, when completely 

 developed, nearly encircle the body ; but it must be 

 admitted that it is not a very happy expression, as, 

 except through the intervention of the vertebral col- 

 umn, they never form complete circles, and very 

 often the " semigirdles " of each side are widely sep- 

 arated both above and below.* 



These girdles and the limbs which they support 

 are never more than two in number on each side, and 

 are almost always placed, the one near the front, 

 and the other near the hinder end of the trunk.t 

 The anterior girdle and limb are often called "pec- 

 toral," and the posterior " pelvic," from the regions 

 of the body in which they are situated. Though in 

 the large majority of vertebrated animals both pairs 

 of limbs are present, either one or the other may 

 be in a very rudimentary condition, or even alto- 



* The semigirdles are sometimes called "arches," which 

 is hardly more expressive, as, though the word means a seg- 

 ment of a circle in any position, the transverse position is 

 now almost universally associated with it. 



t In some fishes the ventral fin, which corresponds to the 

 hind limb of most vertebrates, is placed below, or even an- 

 terior to the pectoral fin, or true front limb. 



