VERTEBRATA. 2^3 



are, in mammals, the scapula, or shoulder-blade 

 (dorsal), and the clavicle, or collar-bone (ventral), 

 while in the Prototherla, or lowest mammals, and in 

 most other Vertebrates, there is also another ventral 

 piece, called the coracoid, and in amphibia and 

 reptiles some additional parts are respectively distin- 

 guished. The pelvic girdle consists of three bones on 

 each side, the ilium (dorsal) and the ischium and 

 pubis (ventral) ; these form the pelvis (Lat. pelvis, 

 a basin), so called from its shape in the human skele- 

 ton. These parts are only found in animals higher in 

 the vertebrate scale than fishes ; but it has been shown 

 that they are in a measure comparable with the bony 

 pieces at the base of fishes' fins. The ordinary verte- 

 brate limb is regarded as derived from a fin type, the 

 bones of the digits being restricted in number anA 

 increased in size. Thus our hands and feet, with five- 

 tolerably similar digits, are less a departure from the- 

 primitive type than the wing of the bird, which re- 

 tains only three digits, or the foot of the horse, which 

 retains practically only one. Besides these must be- 

 named the branchial skeleton {i.e. skeleton of the- 

 gills, Grk. ^pdyx^ia, gill), which, though very small in 

 the reduced state in which it exists in the higher 

 Vertebrata as the hyoid bone (see p. 246), is yet 

 very important, on account of the light that its de- 

 velopment throws upon the relationship of the various 

 groups of Vertebrates. 



The Vertebrates have various features which mark 

 them as metameric or segmented animals, e.g., the 



