476 On the Nervous Systems of 
the animal economy. Numerous instances might 
be adduced, wherein one, or more of the most 
important organs of the human body have been 
found wanting in the fetal state. But, passing 
over the defects, which occasionally take place 
-in the organs of respiration, circulation, diges- 
tion, generation, &c, I shall in this paper con- 
fine myself to the consideration of the defects, 
observable in the nervous system of man, and 
their influence on the important faculties of 
sensation and voluntary motion ; premising some 
general observations on the diversity of parts, 
structure, substance, texture, proportion, laws, 
&c, of the nervous system of man and the inferior 
animals in their natural, or perfect state, 
§ 1. 
On the Nervous System in the different classes of 
Animals. 
By acelebrated modern writer on Comparative 
Anatomy, M. Cuvier, animals are referred to 
two grand divisions: The first comprehending 
all those, which havea dorsal spine, or vertebre: 
The second comprehending all those, which are 
destitute of vertebre. 
To the former division are referred the first 
four Linnean classes of animals, namely, Mam- 
malia, Aves, Amphibia, and Pisces. To the latter 
belong the two remaining classes of Jnsecta and 
