812 COMPARATIVE. HISTORICAL. 



which thick nerves pass off corresponding to the main trunks of the water-vas- 

 cular system. At the point of origin the nervous ring is provided with the 

 so-called ambulacral brains. Arthropods possess above the pharynx a large cephalic 

 ganglion from which the sense-nerves arise. Another ganglion below the pharynx 

 is connected on each side with the first by means of a commissure. From this 

 point the abdominal chain of ganglia extends through the thorax and the abdomen. 

 At times several ganglia are fused into a nervous node of considerable size; at 

 other times they remain isolated for the majority of the segments of the body. 



In molluscs also the pharyngeal ring is still present, although the ganglionic 

 masses occupy a varying position in it. A number of remotely situated ganglia 

 connected with the pharyngeal ring by means of filaments represent the sympa- 

 thetic. In cephalopods a portion of the pharyngeal ring almost entirely devoid 

 of commissures is enclosed as the brain in a cartilaginous calvarium. In addition 

 ganglia are found in the stomach and the heart. In vertebrates the nervous 

 system is always situated on the dorsal aspect of the body. In the amphioxus 

 it is not yet subdivided into brain and spinal cord. The divisions of the brain 

 of vertebrates have been discussed on p. 776, the peripheral nerves on p. 721. 



Historical. Alkmaeon (580 B. C.) located consciousness in the brain, Galen 

 (131-203 A. D.) the impulse for voluntary movements.' Aristotle (384 B. C.) 

 described the brain of man as relatively the largest. He designated it as unirri- 

 table to stimuli (insensitive). He considered small persons as mentally superior. 

 He considered it a function of the brain to cool the heat arising from the heart. 

 Herophilus (300 B. C.) properly considered the region of the posterior horn as 

 the principal seat for sensation. He described, further, the calamus scriptorius. 

 Probably as a result of experiment, he considered the fourth ventricle as the 

 most important for life. Homer makes repeated references to the danger of 

 injury of the neck (the seat of the medulla oblongata). Hippocrates, Galen, 

 Aretaeus, and Cassius Felix (97 A. D.) knew that a lesion of one-half of the brain 

 causes paralysis on the opposite side of the body. Galen recognized the spinal 

 cord as containing the conducting tract for motion and sensation. The ascetics 

 of the Middle Ages were familiar with visual hallucinations (visions) and the like, 

 and many important paintings are to be considered as representations of such 

 hallucinations, the eye of the expert now and again recognizing in them photoptic 

 secondary phenomena, for example scintillating scotoma. Vesalius described 

 (1540) the five ventricles of the brain. R. Columbo observed (1559) the move- 

 ment of the brain synchronous with the action of the heart, while the respiratory 

 movement of the brain was first described accurately in 1811 by Ravinna. Varo- 

 lius (born 1543) described the pons. Goiter noted (1573) the possibility for life 

 to continue after removal of the cerebrum. Wepfer discovered in 1658 the 

 hemorrhagic nature of apoplexy ("sanguine extra vasa effuso ex rupto ramo"), 

 while Sylvius de le Boe described the fossa and the aqueduct named after him. 

 Schneider (1660) determined the weight of the brain of different animals. Mis- 

 tichelli (1709) and Petit (1710)- described the decussation of the fibers of the 

 medulla below the pons. Haller and his pupil Zinn were familiar with the cir- 

 cular movements following injuries of the brain. Lorry was the first to observe 

 disorders of coordination in a pigeon after puncture of the cerebellum (1760). 

 Gall demonstrated the partial origin of the optic nerve from the anterior quad- 

 rigeminate body and he gave the best descriptions of the fibers and of the convolu- 

 tions of the brain from dissection of the brain from below. Luigi Rolando (1809) 

 described the great central fissure of the brain. He and Bellinger (1823) described 

 more fully the form of the gray matter of the spinal cord. Carus described (1814) 

 the central canal of the spinal cord, which had already been observed in the 

 seventeenth century by J. Conrad Brunner. A most extensive anatomical 

 work upon the brain was written by Burdach (1819-1826). 



