INTERNA! STRUCTURE OF THE BRAIN STEM 1041 



This was indeed a critical niodHKatioii. It established beyond cjuestlon the 

 great ]:)artlnij; ot the \\a\ s between the antliiDpoid and the lumian, raising an 

 efTectual barrier betwxx'n the one knul and the other. It was tlu' decisive 

 inllueiiee w Inch turiied the course ol the a])es to then' o\\ n specilic exohitional 

 tcrnilnl,]:)uttnig man upon his course which, through \ arlous stages of progress, 

 has led to his ])resent estate. What the underlying nioti\e ol this critical 

 modllication may ha\e been is still clouded in obscuritw I In' increasing 

 weight of the body appears to ha\c jjlayed some role in this alteration. For 

 it was unquestionabl\ the de\'elopmcnt ol ci-rtain inconx enK'iices and dis- 

 acKantages in arboreal liti' that cxcntuallx brought someol the primate stock 

 nearer to the ground and linall\' brought about the change in the lowx'r 

 cxtremit\' resulting m tlu' inception ot the human loot. 



Probable Role of Endoc:ri\e Glands. TIu' lactors \\ ha h ma\ ha\e 

 increased the bod\" \\eight and so necessitated this change Irom arbort'al to 

 terrestrial lite are dithcult to estimate. It is possible that the indocrinc 

 glands had some part in this alteration. Changes in then" acti\'it\ may have 

 so altered the metabolism ol the body as to jjroduce that degree of maero- 

 somia which is no longer adapted to tree-dw cllmg. From pathological evi- 

 dence it is recognized that enlargements m the ])ituitary gland produce the 

 condition in man termed gigantism. Many ol tlu- more or less monstrous 

 extravagances m statural growth seen olteii-tmies in (.'\hibit ions and known 

 the world oxer as giants are the results of h\pertro|)h\ m the glandular 

 ])ortion of the ])itiiitar\- bod\ . That such hypertrophy may well account 

 for an increased secretion in this gland and thus ])roduce exuberant growth 

 m the long bones is an accepted clinical lact. So also is the disease known 

 as acromegaly in which, alter adolescence, certain mdi\ iduals manilest a 

 tendency toward increased growth in the hands and in the feet, in the face 

 and other portions ol the bon\- skeleton, due to alterations in the pituitary 

 gland. Another group of facts pointing in the same direction are those coipo- 



