364 NERVOUS SYSTEM OF VERTEBRATA, | 
Charles Bell, that the posterior set of roots consists of thos 
fibres that bring impressions from the body in general to t thi 
_ Spinal Cord ; which impressions, if carried-on to the Brair 
convey motor influence es the Spin nd 
Cord and Brain, to the muscles of the bod: 
Thus if the spinal cord of an animal | : 
touched, acute pain is obviously produced 
whilst, if the anterior roots be irritated 
violent motions of the muscles supplied bj 
that nerve are occasioned. Both thes 
Fig. 191.—Portiox op roots contain fibres that ‘connect them wit 
Fine lip mga! , the brain as well as with the spinal cord’ 
the nerves: a, spinal SO that, through the same trunk, either o 
orvinghon upon it, ese centres may act upon the part. W 
course; d, anterior shall presently find that there is go 
rhicunion ofboth, Teason to believe the Brain to be the sei 
J, branch. of sensibility and of voluntary power ; whi 
the Spinal Cord is the instrument of those reflew actions which 
take place automatically, as it were, without direction on the 
part of the animal, and which are concerned in the mainte 
nance of the organic functions of the body, and in its preser 
vation from injury. 
452. The relative proportions which these different parts 
present, are very different in the several classes of Vertebrata) 
We find that among the lower, the Sensory Ganglia, or gai 
glionic centres immediately connected with the organs of sensi 
(which are analogous to the cephalic ganglia of the Invertebrata) 
are very large, and occupy a considerable part of the cavity of thy 
skull ; whilst the Cerebrum and Cerebellum are comparativel 
small. ~The Cerebrum increases, as we ascend the scales L 
proportion to the development of the intelligence, and thy 
predominance which it gradually acquires over blind unde 
signing instinct (Chap. x1v.). Its greatest development 1) 
seen in Man.—The Cerebellum seems to be connected wit 
muscular motion, and to bear a proportion in size with th 
variety and complexity of the movements which the an imé 
performs, serving to harmonise these and blend them togethe 
(§ 480). On the other hand, the Spinal Cord, and the nervi 
