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, 1 who, from a 



1 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. 



