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THE 
AMERICAN NATURALIST 
VoL. XAV. FEBRUARY, 1891. , 291. 
RECENT STUDIES OF THE VERTEBRATE HEAD. 
BY H. W. NORRIS. 
HE view that the vertebrate head is composed of several seg- 
ments, comparable to those of the trunk, has of late years 
formed the basis of almost innumerable essays; but the problems 
connected therewith cannot yet be regarded as solved. It is, 
indeed, universally admitted that the head is composed of seg- 
ments or metameres; but the number of segments and the limit 
of each segment are points upon which there is far from una- 
nimity of opinion. A study of the skull, as was first pointed out 
by Goethe, leads to one conclusion, while a study of the muscle- 
plates or myotomes of the embryo gives greatly different results. 
Then the brain itself in its early stages shows marked evidence of 
metamerism, while the nerves arising from the brain can be more 
or less clearly divided into segmental groups which can be com- 
pared to the undoubtedly segmental spinal nerves. 
In the following pages I have presented, in a very condensed 
form, the results of some recent studies in this direction. In these 
abstracts the nerves are referred to by Roman numerals, in accord- 
ance with the commonly received ideas of their sequence: I., 
olfactory; II., optic; III., oculomotor; IV., trochlearis ; V., tri- 
geminus; VI., abducens; VIL, facial; VIIL, auditory; IX., 
glossopharyngeal; X., vagus; XI., spinal accessory ; XII., hypo- 
glossal. 
In the lizard, according to Hoffmann ('88-'89), the myo- 
tomes of the head agree very closely with the same in the chick 
