130 ERECT ATTITUDE OF THE SKELETOX. 



over the ankle-joint is more immediately necessary. But at the knee and hip- 

 joint, it is mainly by the mechanism of the ligaments and other parts of the 

 joints, and less directly by muscular action, that the erect attitude is maintained, 

 as will be more fully shown in the description of the different articulations. 



There are, besides, many peculiarities in the construction of the body, and 

 esi^ecially of the skeleton, which arc associated with the assumption of the erect 

 l^osture, and although many of them have been noticed in the description of the 

 several sets of bones, it may still be useful to recapitulate them briefly in this i:)lace. 

 It may first be remarked that the full development of these iDCCuliarities 

 belongs to the adult condition. In the infant, while still unable to walk, the 

 large proiiortional size of the head, amounting to nearly a fifth of the whole 

 body, the comijarative straightness of the vertebral column, or absence of the 

 curves which characterise the si^ine of the adult, the shortness of the lower limbs, 

 and incompleteness of theii' structures, all contribute to render the assumj^tion 

 of the erect attitude by the child, for a time, difficult and insecure. Thus the 

 middle distance between the vertex of the head and the foot in a child is 

 situated somewhat above the umbilicus, while in the adult it is generally at the 

 upper border of the pubis, or even lower in some jiart of the symphysis. In the 

 child also, from the large dimensions of the head and iipper part of the body, the 

 centre of gravity is carried to a considerably higher point than in the adult. 



The skull of man differs from that of animals in being nearly balanced on the 

 vertebral column, the condyles of the occipital bone l^eing brought forward to 

 near the middle of the base, by the comparative shortness of that part of the 

 skull which lies in front of the foramen magnum, and the projection backwards 

 of that which lies behind it. In animals the skull hangs forwards, as it were, 

 from the extremity of the column, and is sustained by the elastic ligamentum 

 nuchas, represented in man by a comparatively feeble structui-e Avhicli passes 

 between the external occipital protuberance, and the spinous processes of the 

 cervical vertebra;. 



The spinal column, by its pjTamidal fonn. is fitted to sustain the weight which 

 bears do\vn upon its lower jiart, and by means of its different curvatui-es possesses 

 elasticity and strength combined, and allows considerable range of motion to the 

 trunk, without removal of the centre of gi-avity from within its base. The 

 strong and exiianded sacrum is the immediate means of transferiing the weight 

 of the trunk to the ossa innominata and lower limbs. 



The pelvis is of peculiar breadth in man, presentmg an upper and lower arch 

 which meet at the hip-joints, and is so inclined that a vertical line descending 

 from the centre of gravity of the body is in a plane slightly behind the centres 

 of motion of the hip-joints. The breadth of the pelvis enables the balance to be 

 more easily mamtamed in lateral movements of the body by compensatmg 

 inclinations of different jiarts to opposite sides of the l^asis of support, and the 

 long neck of the femur gives an advantageous insertion to the muscles by which 

 the balance of the body is principally jireserved. The os innominatum is mainlj' 

 distmguished from the same bone in animals by the breadth of its iliac portion, 

 which gives support to the abdominal viscera, and attachment to the greatly 

 developed iliac and gluteal muscles. 



The lower lunbs are remarkable for their length and strength. The femiu- is 

 greatly elongated, its length considerably exceeding that of the tibia, — a condi- 

 tion which is requisite not only to give a sufficient extent of stride, but also to 

 enable the body to be balanced in different degrees and varieties of stooping. 

 The foot of man alone among animals has an arched instep, and it likewise 

 presents a great In-eadth of sole. The great toe is distinguished by its full 

 development, and especially from that of the quadi-umana, by its want of 

 opposability, being constructed, not for graspmg, but for supporting the weight 

 of the body, and giving spring to the step. 



AMiile stability and strength are thus provided in the lower limbs, mobility and 

 lightness are secured in the upper. This is apparent on comparison of the 

 shoulder, elbow, and wrist, with the hip, knee, and ankle. In the hand, also, 

 the movable phalanges are as long as the cai-pal and metacarpal bones taken 

 together, while in the foot they are not a thii"d of the length of the tarsal and 

 metatarsal Ijones. 



