GENERAL CHARACTERS OF THE VERTEBRATA. 377 



series of bones which also correspond to one another in general 

 structure. The fore-limbs, often called the " pectoral " limbs, 

 are united with the trunk by means of a bony arch, which is 

 called the "pectoral "or " scapular " arch ; whilst the hind- 

 limbs are similarly connected with the trunk by means of the 

 " pelvic arch." In giving a general description of the parts 

 which compose the limbs and their supporting arches, it will 

 be best to take the case of a Mammal, and the departures 

 from this type will then be readily recognised. 



The pectoral or scapular arch consists usually of three 

 bones, the " scapula " or shoulder-blade, the " coracoid," and 

 the " clavicle " or collar-bone ; but in 

 the great majority of the Mammals, the 

 coracoid is anchylosed with the scap- 

 ula, of which it forms a mere process. 

 The scapula or shoulder-blade (fig. 

 1 56, s) is usually placed outside the ribs, 

 and it forms, either alone or in con- 

 junction with the other bones of the 

 shoulder-girdle, the cavity with which 

 the upper arm is articulated. The 

 coracoid, though rarely existing as a 

 distinct bone in the Mammals, plays a 

 very important part in other Verte- 

 brates, as we shall see hereafter. The 

 clavicles are often wanting or rudi- 

 mentary, and they are the least essential 

 elements of the scapular arch. The 

 fore-limb proper consists, firstly, of a 

 single bone which forms the upper arm, 

 and which is known as the humerus 

 (h). This articulates above with the 

 shoulder-girdle, and is followed below 

 by the fore-arm, which consists of two 

 bones, called the radius and ulna. Of 

 these the radius is chiefly concerned 

 with carrying the hand. The radius 

 and ulna are followed by the bones of 

 the wrist, which are usually composed 

 of several bones, and constitute what is 

 called the carpus (d). These support 

 the bones of the root of the hand, which 

 vary in number, but are always more or 

 less cylindrical in shape. They constitute what is called the 

 metacarpus. The bones of the metacarpus carry the digits, 



Fig. 156. Pectoral limb 

 (arm) of Chimpanzee. 

 (After Owen.) c Clavi- 

 cle ; J Scapula or shoul- 

 der-blade ; k Humerus ; 

 r Radius ; Ulna ; d 

 Bones of the wrist, or car- 

 pus ; in Metacarpus ; p 

 Phalanges of the fingers. 



