384 THE NERVOUS SYSTEM IN GENERAL, [ch. ii. 



bellum, from which the nerves directly arise ; and, thirdly, the 

 nerves distributed from the general sensorium to all parts of 

 the body. 



SECTION II. HOW THE NERVOUS SYSTEM IS CONSTITUTED IN 



OTHER ANIMALS, AND HOW FAR IT EXTENDS THROUGH THE 

 WHOLE ANIMAL KINGDOM. 



That the nervous system is not constituted in all animals as 

 in man, is proved by the observations of eminent men; but 

 all the differences which the almost innumerable species of 

 animals present, have not as yet been fully investigated : to 

 observe and tabulate all would require almost an age, although 

 much light might be hoped to be thrown by them upon the 

 functions of the nervous system. Many of the able observers, 

 who have undertaken the investigation of these differences by 

 means of comparative anatomy, have directed their attention 

 solely to the cerebrum, and the sum of their observations has 

 been set forth by Ludwig, in his dissertation ' De Cinerea Ce- 

 rebri Substantia.' For the sake of brevity, I will only glance 

 at the more manifest differences derived from the trustworthy 

 observations of distinguished men. 



Man has the largest brain ; all other animals have less, except 

 certain apes, in which the brain is not less proportionally than that 

 of man.^ In fishes and animals of cold blood, the brain is so 

 small, that some writers have not hesitated to look upon it as only 

 an appendix to the spinal cord. There is a great difference in 

 the structure and composition of the brain of animals : in many 

 the olfactory nerves are thick and hollow, and termed mam- 

 millary processes, while the contrary is observed in man ; the 

 convolutions are absent in dormice and birds ;^ in birds and 

 fishes, the thalami nervol'um opticorum are hollow and distinct 

 from the cerebrum ; birds and many fishes have no true corpus 

 callosum, or fornix, or pineal gland; according to the obser- 

 vations of Haller,^ birds and fishes have bodies similar to the 

 corpora quadrigemina, but of simpler character than those of 

 quadrupeds. Other divisions of the brain, as the medullary and 



' Haller, de Part. Corp. Hum. Fab., torn. vii. 



2 Ludwig, Diss. cit. 



' Oper. Mill., torn, iii, p. 214. 



