DISUSE AND ITS EFFECTS. 51 
by a similar method a nether opening, the anus, is 
established. The intermediate section becomes the 
permanent alimentary canal. The walls of the dorsal 
section of the tube thicken, the cavity becomes restricted, 
and the bend connecting it with the ventral tube atrophies, 
thus disconnecting the two limbs; the dorsal portion 
finally developes into the brain and spinal cord. The 
various connecting parts are represented in the adult by 
the following structures, diagrammatically indicated in 
fig. 25. The diverticulum, P, is the infundibulum ; this 
was closely associated with the primitive gullet. The 
connecting limb, N,completely disappears, but the section 
of the gut into which it opens is represented by a small 
pedunculated body at the extreme end of the vertebral 
column, and known as the coccygeal gland. The dorsal 
and ventral limbs of these tubes in the adult are con- 
nected in a subtile manner by means of nerves. The 
walls of the dorsal tube contain collections of nerve-cells, 
from which nerves issue, portions of which are distri- 
buted to the body walls, others of peculiar character 
ramify in the walls of the intestines and are intimately 
associated with its nerve plexuses. 
This view as to the intestinal origin of the central 
canal of the nervous system receives admirable support 
from the investigations of Dr. Gaskell,t who, from a 
™ My conclusions were framed in July, 1887, and briefly stated to 
the Pathological Society in October of that year. My manuscript 
was sent to “ Brain ” in August, but owing to the unfortunate illness 
of the Editor it was not published till January, 1888. Gaskell 
states that he framed his conclusions in the summer of 1887, but 
_he did not mention them in public till June, 1888, and did not 
publish them till April, 1889. 
