GENERAL CHARACTERS OF THE VERTEBRATA. 331 



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. 119, s) 

 is usually placed outside the ribs, and 

 it forms, either alone or in conjunction 

 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 Vertebrates, as we shall 

 see hereafter. The clavicles are often 

 wanting, or rudimentary, 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 arti- 

 culates 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 fol- 

 lowed 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. 119. Pectoral limb 

 (arm) of Chimpanzee. 

 (After Owen). c Cla- 

 vicle ; ^ Scapula or shoul- 

 der-blade ; h Humerus ; 

 r Radius ; Ulna ; d 

 Bones of the wrist, or car- 

 pus ; m Metacarpus ; p 

 Phalanges of the fingers. 



