NERVOUS SYSTEM OF VERTEBRATA. 119 



food, the control of the locomotive apparatus seems to be placed. Now, in the 

 Vertebrata we have the locomotive powers of the Articulata (comparatively 

 reduced, however, in activity"), united with the complex nutritive system of 

 the Molmsca ; and we find this combination manifested, not only in the organs 

 themselves, but in the Nervous System, which stands in so close a relation 

 with them. The Spinal Cord of Vertebrata is evidently the analogue of the 

 ventral columns of Articulata. It is a continuous ganglion, containing two por- 

 tions as distinct as the two tracts in the Articulata; a fibrous structure, which 

 is continuous between the Brain and the spinal nerves, and thus resembles the 

 white tract in Insects; and a ganglionic portion, principally composed of 

 gray matter. Into this gray matter, as in the ventral ganglia of Insects, a part 

 of the roots of the spinal nerves may be traced ; whilst others pass on continu- 

 ously to the brain. At the upper extremity of the Spinal Cord (commonly 

 termed the Medulla Oblongafa), we find the ganglia and nerves of special 

 sensation ; and the organs which these supply are placed in immediate proxi- 

 mity with the entrance to the alimentary canal, holding the same relation to 

 it as in the Mollusca. But in addition to these, we find two ganglionic masses 

 in all Vertebrata, to which we have no distinct analogue in the lower classes 

 the Cerebral Hemispheres, and the Cerebellum. With the development of the 

 former of these, the perfection of the reasoning powers appears to hold a close 

 relation ; that of the latter seems connected with the necessity which exists 

 for the adjustment and combination of the locomotive powers, when the variety 

 of movements performed by the animal is great, and the harmony required 

 among them is more perfect. Upon these points, however, we shall hereafter 

 dwell. 



159. The Visceral system of nerves now assumes a more distinct form. 

 It does not share the protection of the Spinal column ; but its ganglia lie for 

 the most part in the general cavity of the trunk. The connections of the 

 Cerebro-Spinal and Sympathetic systems may be best studied in the trunk ; 

 since the regularity of the distribution of the spinal nerves prevents the exist- 

 ence of that doubt regarding the nature of the communication which obscures 

 the relation of the cranial nerves with the sympathetic. The great visceral 

 ganglia the cardiac and semilunar, may probably be regarded as the true 

 centres of the Nervous system of Organic life ; whilst the chain of ganglia, 

 which lie along the spine, are intermediate between these and the cerebro- 

 spinal system. When the filaments connecting these ganglia with the roots 

 of the spinal nerves are closely examined, they are found to contain both kinds 

 of fibres ; and they can no more, therefore, be regarded as the roots by which 

 the sympathetic system arises from the cerebro-spinal (as they were formerly 

 considered), than as the roots by which the latter originates from the former. 

 The white tubular fibres which these filaments contain, are found, upon close 

 examination, to be derived from both roots of the spinal nerves, and not from 

 the posterior only, as some have supposed. The quantity of white fibres in 

 the nerves proceeding from this lateral chain of ganglia, is much greater than 

 that contained in the nerves of the solar plexus ; and it is confirmatory of the 

 idea just stated (that the visceral ganglia are the true centres of the sympa- 

 thetic system), to find that the nerves proceeding from them are almost entirely 

 composed of the fibres characteristic of this system ( 110). A few visceral 

 fibres may be found in almost all the Cerebro-spinal nerves; they are particu- 

 larly abundant, however, in the first division of the Fifth pair. It would seem 

 that only a part of these are derived immediately from the sympathetic nerve ; 

 and that the remainder may be traced into the gray matter of the ganglia, 

 formed on the posterior roots of the spinal nerves, and on the larger root of the 

 fifth pair. As this gray matter consists of nucleated globules, like those which 

 are found in the centres of the Sympathetic system, it may be surmised that 



