The projection of the forebrain on the pons and cerebellum

Abstract

The condition was examined in monotremes, marsupials, primitive Eutheria[long dash]especially mice[long dash]and in primates[long dash]especially man[long dash]and the gross anatomy of the pons and cerebellum was studied in most mammalian orders. Monotremes lack frontal cortex and fronto-pontine pathways; hence there is abortion of the pretrigeminal part of the pons, and poor development of the declive-tuber complex of the cerebellum. In most marsupials and in many primitive Eutheria temporo-pontine connections are few with resultant absence of any retrotrigeminal pontine development and rudimentary condition of the culmen complex of the cerebellum; but in these animals the pretrigeminal part of the pons is large and the declive-tuber complex in the cerebellum conspicuous. It is considered that in higher animals and man the frontal cortex is connected chiefly with the frontal part of the pons whence impulses are relayed to the declive-tuber complex of the cerebellum; that the temporal cortex is connected chiefly with the retrotrigeminal part of the pons for relay to the culmen complex of the cerebellum. There appears to be some overlap of representation. The cerebellum is considered as comprising only ant. and post, lobes separated by the fissura prima. The fronto-pontine pathway appears to be related to the release of muscles from the rigidity of the standing posture when they are required for action. The temporo-pontine connections respond to the need for coordinated muscular reaction to the information received by the tactile, proprioceptive, equilibratory, vibratory, auditory and visual senses; in some mammals one or more of these avenues may be developed to the neglect of the others.