VERTEBRATA: GENERAL CHARACTERS. 



451 



lates with the skull, not directly, but by the intervention of a 

 special bone, known as the " quadrate bone " or os quadrat um. 



As regards the limbs of Vertebrates, whilst many differences 

 exist, which will be afterwards noticed, there is a general 

 agreement in the parts of which they 

 are composed. As a rule, each pair of 

 limbs is joined to the trunk by means 

 of a series of bones which also corre- 

 spond to one another in general struc- 

 ture. 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 simi- 

 larly connected with the trunk by means 

 of the " pelvic arch." In giving a gen- 

 eral description of the parts which com- 

 pose 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 scapula, 

 of which it forms a mere process. The 

 scapula or shoulder-blade (fig. 242, s) is 



usually placed outside the ribs, and it Fig. 2 4 2.-Pectorai limb (arm 

 forms, either alone or in conjunction with 

 the coracoidal element 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 ele- 

 ments of the scapular arch. The fore-limb proper consists, 

 firstly, ^of a single bone which forms the upper arm (or 

 " brachium "), and which is known as the humerus (h). This 

 articulates above with the shoulder-girdle, and is followed 

 below by the fore-arm (or " antibrachium "), which consists of 

 two bones called the radius and ulna. Of these the radius is 

 chiefly concerned with carrying the hand (or " manus "). . The 



of Chimpanzee (after Owen). 

 c Clavicle ; j Scapula or 

 shoulder-blade ; h Humerus ; 

 r Radius ; u Ulna ; d Bones 

 of the wrist, or carpus; m 

 Metacarpus ; / Phalanges of 

 the fingers. 



