M A M M A L I A. 



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. This is a part of the structure in which mammalia 

 differ from each other, and also from birds ; and, 

 then-fore, it must be well attended to. The two 

 extremes of articulation for the shoulder, or rather of 

 affording a support for its articulation, may be con- 

 sidered the nearest approximation to absolute rest on 

 the one hand, and that which admits of free motion 

 in the mesial plane, without any cross bone applied as 

 a strut or tie, to restrict the motion of the glenoid 

 cavity ; that is, of the humeral end of the blade-bone 

 on the other. The first is what we find in birds. In 

 them the motion of flying, which is the essential 

 motion of the anterior extremities of the class, not 

 only does not require a free motion of the glenoid 

 cavity ; but it requires that this cavity should be as 

 nearly as possible fixed in its position upon the body 

 of the bird ; because the powerful stroke which a 

 winy: requires to take in order to send a bird rapidly 

 throug-h the air, is inconsistent with any considerable 

 degree of shake in the first joint of the wing. If 

 motion proceeding or produced from any fulcrum, is 

 to be vigorous and effective in proportion to the 

 whole muscular force exerted, this fulcrum must be 

 firm ; and yet it is inconsistent with the contents of 

 the chest, even in a bird, that the wing-joint should 

 be articulated directly upon the walls of that. A 

 tripod is therefore (see the article BIRD), provided 

 for the articulation of the wing, and this tripod is 

 firm, and bears equally upon its three branches in 

 proportion as the action of the wing is to be vigorous. 

 The three branches of the tripod ; first, the blade- 

 bone, placed on the upper part of the shoulder as in 

 the mammalia, but more simple in its form, and less 

 abundantly supplied with muscles ; the coracoid bones, 

 which connect the heads of the scapulars with the 

 anterior angles of the sternum, and which, though se- 

 parate bones and differently arranged, bear some 

 analogy to the coracoid processes in mammalia ; and 

 the fucal bone which is applied to the heads of the 

 blade-bones and coracoids, and keeps them asunder. 

 This is the bone which answers to the clavicles in 

 mammalia; and, as is the case among them, it is the 

 bone which varies the most in form and strength 

 according to the different kinds and degrees of action 

 of the wing. The opposite extreme may be 

 regarded as that in which the shoulder-blade has 

 a free and extended motion, untrammelled by any 

 connecting bone ; this is the characteristic form in 

 galloping animals, as in horses for instance. The 

 blade-bone, though embedded in the flesh in these 

 cases, may be said to be a part of the acting limb ; 

 and thus, in animals which are unfettered with clavi- 

 cles in this part, the whole muscles of the shoulder 

 come into play in the same action ; and the spinous 

 processes of the dorsal vertebrae form the points of 

 support for the first series of muscles that come into 

 play in the rapid motion of the limb. The human 

 subject is intermediate between them ; and the gle- 

 noid cavity can be moved round in a circle, though 

 the chief motion is in the blade-bone, in consequence of 

 its being free at its distal extremity from the joint, 

 whereas the clavicle is tied to the sternum. The hu- 

 merus, shoulder-bone, or more correctly the arm-bone, 

 is connected with tne blade-bone only at its upper 

 extremity, It forms the strongest part of the arm, 

 and has two tubercles, and also condyles on the ex- 

 mity, most distant from the body. The two bones 

 of the fore-arm are the ulna and radius. The ulna 

 forms the elbow joint with the hnmerus, and the 



radius acts against a tubercle, and gives a twisting or 

 rotatory motion to the hand. Both these bones have 

 cavities at their extremities for receiving the processes 

 of those bones with which they are articulated ; but 

 they have also projecting processes which increase the 

 lever power of the joints, and ridges in their length 

 which give firm insertion to the muscles. The chief 

 muscles that move the fingers as a whole, have their 

 insertion on these bones. 



It is scarcely possible to give a popular account of 

 the bones of the wrist so as to make the mode of their 

 action intelligible to ordinary readers. Generally 

 speakiner, they have sliding motions ; and those mo- 

 tions are secondary, or only modifications in the 

 direction of such motions as are communicated to 

 the hand. With the exception of that one of the 

 number which answers to the thumb, the metacarpal 

 bones, that is, the bones of the palm, have compara- 

 tively little proper motion. Their chief purpose 

 seems to be to support the tendons which move the 

 fingers and thumb, and to afford a more extensive 

 grasp. The latter use of them is illustrated by the 

 fact that those mammalia whose hands are more 

 exclusively grasping instruments, and not instruments 

 of all work like the human hand, have this part of 

 the structure more extended, and they grasp more 

 firmly in proportion to their size than the human 

 hand can grasp. The principal motions of the pha- 

 langes of the fingers and thumb are opening and 

 shutting ; but the fingers have some rolling motion 

 on those joints by which they are articulated to the 

 palm ; so that a small circle may be described with 

 the point of the finger, while its articulation with the 

 palm, that is, the point to which it is articulated, re- 

 mains perfectly at rest. This motion is more free in 

 the fore finger than in any of the other three ; and it 

 is comparatively very free in the thumb, which is 

 articulated upon a sort of universal joint, only it does 

 not in a stiff hand extend far backwards. We shall, 

 however, have occasion to speak of some of the 

 articulations afterwards. The bones of the lower 

 extremities have been in part already mentioned. 

 The thigh bone is connected at its lower extremity 

 with the upper end of the tibia, or principal bone of 

 the leg ; and the knee-pan lies over and strengthens 

 the articulation in the manner which has been already- 

 described. The knee-joint between the thigh bone 

 and the tibia is a hinge, formed by two processes of 

 the upper bone acting in two cavities ; and the head 

 of the tibia is enlarged, in order to adapt it the better 

 to the enlarged processes of the thigh bone. The 

 external part of the head of this bone is the most en- 

 larged ; and to the enlargement of this the head of 

 the fibula, or small bone of the leg, is applied ; and 

 this gives a slight twisting motion to the knee. The 

 distal extremity of the tibia embraces the astragalus, 

 or great articulating bone of the foot, on its upper 

 surface, and also on its inner side, where an extended 

 process forms the inner projecting bone of the ankle. 

 The lower extremity of the fibula is applied on the 

 other side, and forms the external projecting ankle 

 bone. The enlarged process of the astragalus which 

 forms the heel, and gives the limb a firm basis while 

 the body is in a horizontal position, or bent in any 

 direction, and still resting firmly on the foot, is pecu- 

 liar to the human subject. The tarsal bones of the 

 foot have sliding motions, something analogous to 

 those of the wrist bones ; and by means of them the 

 foot can adapt itself to many forms of surface, and 



