462 B. F. KINGSBURY 
The His conception fitted in excellently with the already well- 
established view of brain segments;! since if the brain is composed 
of three ‘primary segments’ in turn divisible into five or six 
‘secondary segments,’ these would only possess a segmental value 
if they were subdivisions of a fundamentally tubular structure 
and were serially comparable and metamerically equivalent. 
His therefore proposed a revision of the subdivisions of the 
brain—partly it is true for nomenclatural reasons—and_ his 
grouping and subdivision of the brain set forth in 1893 is the one 
generally accepted and the usual basis for text-book presentation 
of the brain. Both Herrick (10) and Johnston (’09) have pro- 
posed modifications of the His schema of brain segments. 
Likewise, the attempt to analyze the neural tube in terms of 
more primitive segments comparable with the somites of the 
mesoderm, the so-called ‘neuromeres’ found in the tubular plan 
of the brain an essential foundation for the interpretation, since 
clearly these could only possess value as primitive neural seg- 
ments if they extended transversely to include the entire tube 
wall. Since to each neuromere there should belong primitively 
a motor and a sensory nerve the problem of the cranial nerves 
is also involved, as well as the ‘primitive segmentation of the 
head.’ 
Since the publication of the papers by His dealing with the 
fundamental plan of the brain there have appeared three definite 
interpretations departing in important respects from his own. 
These are, in sequence, those of Johnston (’09), Schulte and 
Tilney (’15), and my own (’20). In order to bring out clearly the 
differences in interpretation and the points requiring verification 
two series of diagrams are presented: 1) of the brain in medial 
1 The history of the interpretation of the brain as a tubular organ composed of 
successive segments is practically coextensive with the knowledge of its develop- 
ment and comparative anatomy. While still earlier observers, apparently note 
the brain vesicles, to von Baer (’37) may be ascribed the recognition of three 
primary and five secondary brain vesicles with the well-known designations of the 
German vernacular—Vorderhirn, Zwischenhirn, Mittelhirn, ete. Huxley (’71) I 
believe introduced technical designations for these. Balfour, Wilder (B. G.), 
His, and von Kupffer each modified the scheme of segmentation in accordance 
with his own conceptions. 
