GENERAL CHARACTERS OF VERTEBRATA. 45 



ing faculty ; and the amount of this bears so close a relation with the deve- 

 lopment of the brain, that it is scarcely possible to regard the two as uncon- 

 nected. In Man, whose brain is far larger in proportion to his size, as well 

 as more complex in its structure, than that of any other animal, the reasoning 

 faculties attain the highest perfection that we know to be anywhere manifested 

 by them in connection with a material instrument ; the instinctive propensities 

 are placed under their subjection ; and all his acts, excepting those imme- 

 diately required for the maintenance of his organic functions, are put under 

 their control. It is to Man, therefore, that what was just now stated, of the 

 predominance of the neryous system in Vertebrata, particularly applies ; but 

 the same may be noticed, though in a less striking degree, throughout the 

 group. Not only is the influence of the nervous system to be traced in the 

 sensible movements which they perform, but also in various modifications of 

 the organic functions, which take place under the influence of particular states 

 of mind, and the occurrence of which there is no reason to suspect in the lower 

 tribes of animals. These are even much more striking in Man than in the 

 lower Vertebrata ; indeed, the comparative slightness of the influence of the mind 

 upon the body, is one of the causes which render the lower Mammalia more 

 able than Man is, to recover from the effects of severe injuries. The Mollusca 

 seem to grow like plants ; their massive organs increasing by their own sepa- 

 rate vitality, and being but little dependent upon each other. Even the act 

 of respiration, which is in most animals performed by a series of distinct mus- 

 cular contractions, is there principally effected through the medium of the 

 cilia which clothe the respiratory surface. 'But in the Vertebrata, the nervous 

 system possesses a distinct and independent rank ; its offices are those which 

 more particularly constitute the active life of the animal ; the organic func- 

 tions have for their chief object, the maintenance of the nervous and muscular 

 apparatus in the conditions requisite for their activity, and, in consequence, 

 all these different kinds of apparatus are so interwoven together, that their 

 mutual dependence is very close. 



35. The foregoing remarks will be found to have an important bearing on 

 the details subsequently to be given, respecting the functions of the nervous 

 system in Man ; and it is desirable to set out with clear ideas on this subject, 

 since there is no department of Physiology, regarding which more error is 

 prevalent. There is no valid reason for believing, that the organic functions 

 in Animals, any more than the corresponding changes in Plants, are dependent 

 on the nervous system for their performance ; but common observation shows, 

 that they are much influenced by it in the higher animals ; and from such a 

 comparison as that which has been just now briefly made, it would appear 

 that the higher the general development of the nervous system, the closer is 

 their relation with it. 



36. This general character of the Vertebrata harmonizes well with what 

 may be observed, on a cursory glance at the structure of their bodies, of the 

 proportion between the organs of Nutritive and those of Animal life. The 

 former, contained in the cavities of the trunk, are highly developed ; but, as 

 in the Mollusca, they are for the most part unsymmetrically disposed. Of the 

 latter, the nervous system and organs of the senses occupy the head ; whilst 

 the muscles of locomotion are principally connected with the extremities : 

 both are symmetrical, as in the Articulata; but, whilst that part of the nervous 

 centres, which is the instrument of reason, is very largely developed, the por- 

 tion which is specially destined to locomotion, together with the muscular 

 system itself, bears much the same proportion to the whole bulk of the body, 

 as it does in the Articulated series. Hence we observe that the Vertebrata 

 unite the unsymmetrical apparatus of nutrition, characteristic of the Mollusca, 

 with the symmetrical system of nerves and muscles of locomotion, which is 



