EMANCIPATION OF THE FORE LIMBS 11 



pushed very far back in the geological record, and when 

 it is so pushed back it leads to a curious group of animals 

 known as the Therapsida, which, presenting a blend of 

 primitive reptilian and primitive mammalian characters, 

 flourished in the Triassic. It was, according to Broom, 

 among the South African members of the Therapsida 

 especially that the limbs became supporting organs, and 

 he has said very definitely that " when the Therapsidan 

 took to walking with its feet underneath and its body 

 off the ground it first became possible for it to become a 

 warm-blooded animal." The change that we have been 

 picturing was, therefore, one which took place very far 

 back in the geological past; and, according to Broom, 

 the supporting limb and the mammalian possibilities 

 made their appearance together, the one being dependent 

 upon the other. The characters of the supporting limb 

 as opposed to the purely propelling, but not suj)porting, 

 limb are so definite that there should be but little hesi- 

 tation on the part of an anatomist in assigning the proper 

 functions to the limbs of any extinct form. But it cannot 

 be said that the geologist, when assuming the r61e of an 

 articulator of the skeletons of extinct monsters, has always 

 shown a nice appreciation of these characters. A visit 

 to the geological galleries of any museum wall reveal 

 instances of animals, the limbs of w^hich are articulated 

 for a function that they had no power to perform. 



Looking broadly at the Mammals, we may say that the 

 preservation and elaboration of the inherited mobility of 

 the fore-limb is an essential for the culmination of evolu- 

 tion. We may also say that this preservation of mobility 

 must start very early, before ancestral mobility had 

 become lost in the development of stability; and that the 

 most successful Mammals must, by some means or other, 

 have preserved and stereotyped this mobility almost at 

 the outset of their mammalian career. Again, we may 

 say that two distinct lines have been followed. Some 

 mammals have perfected the new, and mammalian, de- 



