MAMMALIA. 149 



extension of the arches from the back of the body of each vertebra, to its spinous 

 process ; and as these have different motive capabilities in each region of the spinal 

 column, the utmost nicety is required in adapting its delicate texture to them at the 

 proper places. The spine has not only to sustain the head and be adapted to the 

 motions of the trunk, but to the position and free action of the limbs and the support 

 of the viscera. In man the degree of flexion of all the cervical vertebra? together is 

 very moderate, very little in the dorsal, but in the lumbar it is considerable, more 

 particularly in the lower. In the baboon the relation of the parts approaches that in 

 man. In many animals which always move on all-fours a great change takes place ; 

 there may be a less or greater capability of bending the neck, but a much greater at 

 the dorsal portion of the spine ; and this is seen in a remarkable degree in the 

 hedgehog, which draws the lower portion of the body towards the upper, when it 

 becomes folded into a ball within the skin. In others the flexion of the dorsal 

 vertebrae is for a very different purpose. In the sow it forms an arch, by which the 

 weight of the young, the extensive mammae, and capacious viscera, are better and 

 more safely sustained. In others, as the jaguar, it allows the spine to be shortened in 

 swift paces, and therefore the hind legs to be brought more forward at each spring 

 than they otherwise could have been ; in such instances there is very little motion of 

 the lumbar vertebrae, which are required to afford a fixed point for the attachment of 

 the muscles concerned in springing forwards. From the examination of the spinal 

 cord in different animals it appears that its dimensions must be proportioned to the 

 quantity of nerves required to proceed from it, and its largest portion must be placed 

 where it cannot be subjected to undue flexion ; and if it be contained in parts having 

 extensive motions, as in the necks of some birds and the tails of various animals, it 

 must have undergone a sufficient diminution in its circumference. 



SPINAL NERVES. There is a general resemblance of the spinal nerves in 

 mammalia to those in man. They vary in number with the vertebrae, and in size and 

 distribution with the extent and shape of the parts receiving them. The number of 

 cervical nerves is the same as in man; the sub-occipital generally emerges from a 

 foramen in the atlas, but in the rest there is not anything remarkable. The number of 



