M A M M A L I A. 



105 



The trunk also admits of subdivision into the ver- 

 tebral column in the middle of the back, the sternum 

 opposite to it on the breast, the ribs in the sides, and 

 the ossa innominata, or unnamed bones, which form 

 the basin of the pelvis. The vertebral column con- 

 sists of twenty-six pieces jointed together, and admit- 

 ting of a vast number of flexures, but not of any great 

 motion in a single joint, excepting in one or two, 

 which we shall mention afterwards. Of these ver- 

 tebrae, or jointed pieces, seven belong to the neck, 

 and are called cervical vertebra; and this number 

 seven is common to all mammalia, whether the neck 

 be long or short. In some of the cetaceous 

 mammalia those vertebrae are so exceedingly short, 

 that the neck appears to consist of thin plates of 

 bone, which have scarcely any motion ; while in 

 some other animals, as in the giraffes for instance, it 

 is exceedingly long, but this is owing to the greater 

 lengths of the vertebrae, and not to any increase in 

 their number. The next part of the column consists 

 of twelve joints, of the back or dorsal vertebrae as 

 they are called, which have less motion upon each 

 other than any of the rest. Then there come five 

 joints of the loins, or lumbar vertebras, after which 

 there are two terminating bones, the sacrum and the 

 coccyx. The breast-bone generally consists of three 

 pieces ; but these are often so united as to appear 

 only one bone. The ribs are twelve on each side, of 

 which the seven which are nearest the head are called 

 true ribs, and the five towards the loins false ribs ; the 

 former are joined both to the processes of the spine 

 and to the sternum, though these are not articulated 

 so as to have one surface moving upon another in 

 either case ; but the union is formed by flexible car- 

 tilage, and the ribs, both true and false, are capable of 

 a limited degree of motion. Properly speaking, the 

 pelvis consists of only two bones, one on each side ; 

 but each is divided into three parts the hip-bone, 

 the haunch-bone, and the share-bone. Thus the 

 number of bones of the trunk varies, according to the 

 view which we take of those bones of the pelvis and 

 the breast-bone. If we count each of these only as 

 single, then there are fifty-three bones in the trunk ; 

 but if we consider them as divided, then there are 

 fifty-nine. 



All the bones that we have now enumerated, and 

 indeed all the bones in the body, are perfectly sym- 

 metrical, whether they exist in pairs, with an entire 

 bone on each side, or whether they are single bones 

 equally divisible in the mesial plane. 



The anterior extremities, which are the arms in 

 man and the fore legs in the other mammalia, con- 

 sist of thirty-two bones each, and the posterior extre- 

 mities consist of thirty, which gives sixty-four in the 

 pair of the former, and sixty in that of the latter. It 

 is convenient for the sake of brevity to call the anterior 

 extremity the arm, and the posterior the leg ; and if 

 this is understood to refer to the mere position of the 

 extremity, and not to the function which it is best 

 fitted for performing, it can occasion no mistake, 

 though applied to all mammalia whatever. There is 

 even an advantage in this general nomenclature, be- 

 cause it lessens the number of mere names, and by 

 necessary consequence increases that of descriptions ; 

 and it also enables us more readily and clearly to see 

 the differences of structure in those parts of animals, 

 and to understand and appreciate those differences of 

 of action, which result from, or are dependent upon, 

 the differences of structure. 



The bones of the arm consist of two uniting bones 

 the one of which is the blade-bone, embedded in the 

 flesh of the back, and joined to the other parts of the 

 skeleton, the ribs chiefly, only by muscles ; and the 

 other is the clavicle or collar bone, which extends from 

 the top of the shoulder to the upper part of the 

 sternum, the latter union being made by means of 

 flexible cartilage ; and thus this bone admits of con- 

 siderable motion in that part of the blade-bone which 

 contains the cavity for receiving the upper part or 

 head of the humerus, or bone of the arm above the 

 elbow. There is only one bone in this part of the 

 arm, and it is the same in the corresponding part of 

 the leg ; and this runs through the whole of the mam- 

 malia. The fore arm, from the elbow to the wrist, 

 consists of two bones ; the wrist, ( carpus), of eight 

 bones ; the palm of the hand (metacarpus) consists of 

 five bones ; the fingers, of three bones each ; and the 

 thumb of two bones. The bones of the fingers are 

 called phalanges, because they are ranged something 

 like a line of warriors in a battle phalanx, when view- 

 ed across the hand ; and when we take them in suc- 

 cession they appear rank after rank. 



As the head of the femur or thigh-bone is articu- 

 lated immediately on the bones of the pelvis, it does 

 not require that support which the arm gets from the 

 blade-bone on the shoulder, and the collar-bone on 

 the upper part of the breast ; but the consequence is, 

 that without flexure of the whole body, the point to 

 which the leg is articulated has not so much motion 

 of its own as that to which the arm is attached. This, 

 however, is a great advantage in the use of the leg, 

 and gives it a stability which it could not have pos- 

 sessed if the point to which it is attached had been 

 move"able as the shoulder is ; and on the other hand, 

 the arm would not have been applicable to very many 

 of those purposes which it can perform well, if the 

 point of its insertion had not been movable, without 

 the whole body being moved along with it. There 

 is not such complete difference between the mobility 

 of the point of attachment of the arm, and the firm- 

 ness of that of the leg, in any animal, that there is in 

 man ; and this is the reason, or at least one of the 

 chief reasons, why man walks so much better in an 

 erect position than any other animal, and also why 

 man can use his hands in so many different positions, 

 while the body remains perfectly steady, though rest- 

 ing on only the part of one foot. 



This is a part of the subject to which the greatest 

 attention should be paid by every one who wishes 

 to understand the action of animals, and why one 

 animal and not another is found inhabiting a par- 

 ticular place, and performing particular operations ; 

 for it is according as the arm or the leg, or both, 

 deviate from this type at their primary articula- 

 tion, that we find them diversified throughout the 

 greater part of their length. If the arm become prin- 

 cipally a leg that is, if it is used for scarcely any other 

 purpose than that of walking the blade-bone is com- 

 paratively loose upon the shoulder, and the collar- 

 bone is wanting or imperfect ; on the other hand, if 

 the leg partakes of the character of an arm, and is 

 furnished with a hand, or more correctly speaking a 

 prehensile foot, it is invariably loosened in the joints, 

 has a wriggling lateral motion, and is comparatively 

 unfit for the proper function of a leg. We shall be bet- 

 ter able to explain this matter, however, when we come 

 to compare the other orders of mammalia with man as 

 this typical animal. The number and arrangement of 



