THE PRIMATES. 3 



a zoological point of view, man's Body marks him out as 

 belonging to the group of Mammalia (see Zoology), which 

 includes all animals in which the female suckles the young: 

 .and among mammals the anatomical resemblances are 

 closer and the differences less between man and certain 

 apes than between man and the other mammals; so that 

 zoologists still, with Linnaeus, include man with the mon- 

 keys and apes in one subdivision of the Mammalia, known 

 as the Primates. That civilized man is mentally far superior 

 to any other animal is no valid objection to such a classifi- 

 cation, for zoological groups are defined by anatomical and 

 not by physiological characters ; and mental traits, since we 

 know that their manifestation depends upon the structural 

 integrity of certain organs, are essentially phenomena of 

 function and therefore not available for purposes of zo- 

 ological arrangement. 



Man however walks erect with the head upward, while 

 the great majority of Mammals go on all fours with the 

 head forward and the back upward, and various apes 

 adopt intermediate positions; so in considering corre- 

 sponding parts in such cases confusion is apt to arise 

 unless a precise meaning be given to such terms as "an- 

 terior" and "posterior." To avoid this difficulty anato- 

 mists give those words definite arbitrary significations in 

 all cases and these we shall use in future. The head end 

 is always anterior whatever the natural position of the 

 .animal, and the opposite end posterior; the belly side is 

 spoken of as ventral, and the opposite side as dorsal; right 

 ..and left of course present no difficulty. Moreover, that 

 end of a limb nearer the trunk is spoken of as proximal 

 with reference to the other or distal end. The words 

 upper and lower may be conveniently used for the relative 

 position of parts in the natural standing position of the 

 animal. 



The Vertebrate Plan of Structure. Neglecting such 

 merely apparent differences as arise from the differences of 

 normal posture above pointed out, we find that man's own 

 zoological class, the Mammals, differs very widely in its 

 broad structural plan from the groups including sea anem- 



