730 COMPARATIVE AND HISTORICAL. 



by pressure. The application of continued slowly increasing pressure compresses the brain 

 (Adamkincicz). 



382. COMPARATIVE HISTORICAL. Comparative. Nerves are absent in the protozoa. 

 Neuro-muscular cells occur in the coelenterata, in the hydroida and medusae, and they are the 

 first indications of a nervous apparatus ( 296). The umbrella of the medusa is covered with 

 a plexus of nerve-fibrils, which at various parts along its margin is provided with small 

 cellular thickenings corresponding to ganglia, and from these, nerve-fibres proceed to the 

 sense organs. Many of the worms possess a nervous ring in the cephalic portion, and in those 

 provided with an intestine a single or double nervous cord, in the form of a ring, surrounds 

 the pharynx. Branches (often two) pass from this into the elongated body, and usually these 

 carry ganglia corresjwnding to each ring of the body of the animal. In the leech, only one 

 gangliated cord is present. In the echinodermata, a large nerve-ring surrounds the mouth ; 

 and from it large nerves proceed, corresponding to the chief trunks of the water-vascular 

 system. At the points where the nerves are given off, the nervous ring is provided with the 

 so-called "ambulacral brains." The arthropoda are provided with a large cephalic ganglion 

 placed above the pharynx, from which nerves pass to the sense organs. Another ganglion lies 

 on the under surface of the pharynx, and is connected with the former by commissures. The 

 pharynx is thus embraced by a gangliated ring, and from it proceeds the abdominal gangliated 

 double chain, along the ventral surface of the body, through the thorax and abdomen. Some- 

 times several ganglia unite to form a large compound ganglion, while, in other cases, each 

 segment of the body contains its own ganglia. In the mollusca, the oesophageal nervous ring 

 is present, although the ganglionic masses vary much in position within it. A number of 

 compound ganglia lie scattered in different parts of the body, and are united by nerves to the 

 former. They represent the sympathetic system. In the cephalopoda, the oesophageal ring 

 has almost no commissure, and a part of the ganglionic matter is enclosed in a cartilaginous 

 capsule, and is often spoken of as a "brain." Additional ganglia are found in the mantle, 

 heart, and stomach. In vertebrates, the nervous system invariably lies on the dorsal aspect 

 of the body. In the amphioxus, there is no separation into brain and spinal cord. (See 

 374 and 375.) 



Historical. Alkmaon (580 B.C.) placed the seat of consciousness in the brain ; Galen 

 (131-203 A.r.) regarded it as the seat of the impulses for voluntary movements. Aristotle 

 (384 B.C.) ascribed the relatively largest brain to man; he stated that it was inexcitable to 

 stimuli (insensible). One of the functions he ascribed to the brain was to cool the heat 

 ascending from the heart. Herophilus (300 B.C.) gave the name calamus scriptorius ; and he 

 regarded the 4th ventricle as the most important organ for the maintenance of life. Even in 

 Homer there are repeated references to the dangers of injuries of the neck. Aretaeus and 

 Cassius Felix (97 a.d.) were aware of the fact that lesion of one cerebral hemisphere caused 

 paralysis on the opposite side of the body. Galen was acquainted with the path in the spinal 

 cord connected with movement and sensation. Vesalius (1540) described the five ventricles of 

 the brain. R. Colombo (1559) observed the movements of the brain isochronous with the 

 action of the heart. A more careful description of these movements was given by Riolan 

 (1618), Coiter (1573) discovered that an animal can live after removal of its cerebrum. About 

 the middle of the 17th century, Wepfer discovered the hemorrhagic nature of apoplexy. 

 Schneider (1660) estimated the weight of the brain in different animals. Mistichelli (1709) 

 and Petit (1710) described the decussation of the fibres of the spinal cord below the pons. 

 Gall discovered the partial origin of the optic nerve from the anterior pair of the corpora 

 quadrigemina, and by dissecting the brain from below, he attempted to trace the course of the 

 nerve-fibres to the convolutions (1810). Rolando described more accurately the form of the 

 grey matter of the spinal cord. Carus (1814) discovered the central canal. The most 

 compendious work on the brain was written by Burdach (1819-1826). The more recent 

 observations are referred to in the text. 



