MAN 189 



—the reflex centers related to these organs and located 

 in the anterior end of the spinal cord became enlarged 

 to give rise to massive ganglia that took the form of a 

 nose brain/ an *eye brain/ and an *ear brain/ which 

 supplemented older gangha— representing a 'visceral 

 brain concerned with the gills, stomach, and other in- 

 ternal organs, and a 'skin brain,' concerned with the 

 elaborate 'lateral line' and other sense organs which are 

 present in the skin of fishes. Because of the linear ar- 

 rangement and segmental distribution of these master 

 gangha, this part of the brain is generally designated as 

 the 'brain stem'; and, because these gangha were fully 

 developed, in the quahtative sense, in the fishes, the 

 brain stem is sometimes called the 'old brain.' 



As the early vertebrates engaged to an increasing ex- 

 tent in crawling, swimming and other movements, an- 

 other ganghon of the central nervous system developed 

 to form the cerebellum, a part of the brain which is 

 concerned chiefly with motor co-ordination and the 

 orientation of the body and its appendages in space, and 

 the functions of which in all animals remain wholly 

 reflex and unconscious. The relationships between the 

 gangha of the brain stem and the distance receptors are 

 beautifully exhibited in the linear' brain of the common 

 dogfish, which is studied by every student of compara- 

 tive anatomy. But the over-all relations of the brain stem 

 and cerebellum have been reconstructed from well- 

 preserved fossil casts in the Devonian ostracoderm 

 Cephalaspis and foimd to have a pattern not very dis- 

 similar from that of the hving lamprey, so that we may 

 conclude that the 'old brain' or brain stem had been 

 shaped in its fundamental features as early as the 

 Silurian, and perhaps the Ordovician period. 



The progressive enlargement of the central nervous 

 system in the anterior end of the body is called 'en- 

 cephalization' (en = in; kephale = head) , meaning, in 

 common parlance, the development of a "brain in the 

 head,' whence the brain is sometimes called the 'enceph- 



