38 ANIMAL PHYSIOLOGY. 



from tlie ground it becomes tightened, because then it is 

 only by muscular effort that the knee is kept straight. 



The femur in man is longer than in other animals; and by 

 the length of this bone, when we stoop with bent knees and 

 resting on the balls of the toes, the pelvis is thrown suffi- 

 ciently backwards to balance the bending of the body 

 forwards (fig. 27). If the thigh bones were short, it would 

 be difficult to pick an object off the ground. 



The pelvis also is short, expanded, and strong : the pillars of 

 bone which convey the weight from the sacrum to the thigh- 

 bones are stouter than the corresponding parts which have 

 110 such function in other animals; and the expanded blades 

 of the iliac bones both give surface for the attachment of 

 the large glutei muscles by which the trunk is extended on 

 the top of the thigh-bones, and also help to support the 

 viscera above them. 



The bodies of the vertebrse increase rapidly in size from 

 the cervical to the last lumbar, so as to bear the accumulated 

 weight which they support; and the transverse processes of 

 the thoracic and lumbar regions are thrown remarkably back 

 on the arch, so as to bring the bodies as much as possiblo 

 forward into the visceral cavity; a circumstance which will 

 at once strike any one who compares even in a cursory 

 fashion the lumbar vertebrse of a rabbit, sheep, or ox, with 

 those of the human subject. In the thoracic region, the 

 ribs, with the exception of the two last pairs, being attached 

 by distinct articulations to the sides of the bodies of the 

 vertebrse and to the transverse processes as well, have a 

 direction backwards as well as outwards given to them, by 

 which, before arching forwards, they include in their circuit 

 two great fossse at the sides of the column, which contain a 

 large part of the lungs. - .- 



Even the peculiarities of the human skull are closely con- 

 nected with the adaptation to the erect posture. It has 

 already been pointed out that in quadrupeds the head is 

 suspended by a strong elastic ligamentum nuchse; and it is, 

 in addition, supported by muscular action; but, in man, the 

 head is balanced on the top of the atlas when he stands 

 erect. This is an arrangement altogether peculiar to man, 

 and is accomplished, in the first place, by the bones of the 



