240 J. B. JOHNSTON, 
however, is not directly between the development of the cere- 
bellum and the size of the limbs, as OsBorn (88) has stated 
the case for the Amphibia. The degree of development of the 
cerebellum stands in relation with the activity of the animal because 
an active life demands a high degree of perfection of the organs of 
sight, hearing, and cutaneous sensation. The size and number of 
these organs are the factors which determine directly the size and 
complexity of the cerebellum. 
6) The PurKINJE cells of the acusticum are connected, by cells 
of transitional character, with the ordinary large cells of the acusticum. 
Their peculiar dendrites have been developed in response to the 
need for making connections with the very numerous fine fibres of 
the cerebellar crest. The same cause has operated in the cerebellum 
where the development of the PURKINJE cells began earlier and has 
progressed farther. 
7) The granule cells of the cerebellum are to be compared with 
the small cells in the dorsal horn of the cord which send their neu- 
rites into the dorsal tracts, where they divide into ascending and 
descending branches. The great number of these cells in the cere- 
bellum is due to the need of coördination of impulses coming from 
many tracts. Those cells whose neurites pass backward in the cere- 
bellar crest retain their primitive function of connecting successive 
segments. 
8) The basket cells of the cerebellum are present in Acinenser. 
Some of them have spiny dendrites like those of the PURKINJE cells. 
9) There is some evidence that a few neurites of PURKINJE cells 
run to the lower olive in Acipenser. A large bundle of fibres which 
are probably neurites of PURKINJE cells descend over the lateral 
surface of the medulla in the position of the pons of higher Verte- 
brates. 
10) The lobus vagi is the center for components which serve 
“organic” or visceral sensory functions, including the fibres to the 
taste buds and end-buds. Apparently all the fibres of these com- 
ponents have essentially the same relations in the vagus lobe. The 
term “fasciculus communis system” may be applied to these com- 
ponents and their center in the medulla, in all Vertebrates. It is 
represented in the Mammalian brain by the fasciculus solitarius and 
the nuclei accompanying it. This system is completely isolated from 
the cutaneous sensory systems in the medulla and cord of all Verte- 
brates. 
