MAN AND THE VERTEBRATE SERIES. 791 



Protection of the body is, to a certain extent, secured by its being 

 inclosed in a bony case, the ribs. It may be thought strange that the 

 advantajje to be derived from this defensive armor is not extended 

 to the whole body. It very probably would be, were there not some 

 active influence opposing it. This influence may be, the necessity of 

 expansion of the ventral surface. Expansion and contraction in the 

 chest are regular and rhythmical, and are secured by the jointed con- 

 nection of the ribs with the breastbone. Expansion in the abdomen is 

 irresrular and at times excessive. Incasement in an inflexible rib-case 

 would, therefore, prove highly disadvantageous. 



Yet no flexible condition can well arise in response to expansions 

 appearing irregularly and often at long intervals. As the ribs, there- 

 fore, could not gain, by selective adajDtation, the proper motive rela- 

 tiojis to these occasional expansions, and as inflexible ribs would be a 

 disadvantage, abdominal ribs have failed to appear. 



The general characteristics of the body being thus necessarily as 

 we find them, and the position, length, joints, and action of the limbs 

 being inevitable results of their purpose, as the organs of animal mo- 

 tion, it remains to trace the origin of the head with its organs. 



The head is simply the carrier of the organs of the special senses. 

 The brain, so far as its secondary action is concerned, might very well 

 be situated in any other portion of the body, but we think it can be 

 shown that the location of the eyes governs that of the brain, and that 

 the head with all its organs is an adjunct of the eyes. 



These important organs necessarily occupy the most elevated part 

 of the body. The outlook is better from this location, and the safety 

 of the animal is thus more assured. An anterior location is also highly 

 desirable, as otherwise the forward-moving animal would be in con- 

 stant peril from obstacles in its path, and would be unable to per- 

 ceive the prey it was pursuing. Also, as the delicate character and 

 exposure of the eyes tend to limit their number, the portion of the 

 body bearing them must be sufliciently flexible to permit vision in all 

 directions. 



All these requirements tend to the production of an anterior, ele- 

 vated organ mounted on a neck of flexible movement, and as long as 

 is consistent with easy support of the weight of the head. The ears, 

 also, are best situated upon this head organ, and in such a position as 

 to adapt them to catch sound from all dii'ections. 



And this position of the eyes and ears necessarily requires the brain, 

 for its fullest effectiveness, to be likewise situated in the head. For 

 the greatest safety follows the quickest warning of danger. But, as 

 is well known, the nerves are slow in their conveyance of sensations. 

 The animal, therefore, whose eyes and ears are nearest the brain be- 



and aid to the venous current are equal. But the fact holds good in all vertebrate ani- 

 mals, that the quantity of blood to be driven to the brain exceeds that to be driven to 

 the lower body. 



