THE 
AMERICAN NATURALIST. 
Voi. xv. — FULY, 1881.— No. 7. 
ORIGIN AND DESCENT OF THE HUMAN BRAIN,} 
BY S, V. CLEVENGER, M.D. 
tesa object of this paper is to present to comparative anato- 
mists certain aspects in the phylogenesis of the spinal cord, 
which culminate in the development of the brain of man. 
The word brain is here used to include only the nerves and 
ganglia of the skull. The term has been applied so loosely that 
Professor Wilder rightly advises its discontinuance from neurolog- 
ical nomenclature. 
Briefly stated, the nerves interrelate the rauscles as the muscles 
interrelate the bones, nerves further are internuncial in conveying 
external or internal molecular vibrations to irritable or contractile 
tissues, 
Biological investigations enable us to approach very closely the 
border land of sensation and molecular physics. While the 
physicist is striving to reduce his laws of sound, heat, light, elec- 
tricity and gravitation to their ultimates, the biologist is meeting 
him over consideration of the forces which control the motions 
of the Ameeba or evolve the animal from the cell. 
In the Journal of the Royal Microscopical Society (Vol. 111, 
No. 1, P. 63, from Arch. Mikr. Anat., xv, 1879, p. 58) are dia- 
§rams of the simplest acoustic and visual cells. These forms of 
nerve cells proceed from a still simpler protoplasmic cell, which, 
according to situation or the influences brought to bear upon it, 
: Read before the Chicago Academy of Sciences, February’, 1881. 
VOL, XV.—No, vir, 36 
