656 FUNCTIONS OF THE CEREBRO -SPINAL NERVOUS SYSTEM. 



in their case being easily accounted for, when it is remembered in how 

 great a degree the general movements of the body are guided by the visual 

 sense. 



523. Functions of the Sensory Ganglia. We have now to consider what 

 deductions may be drawn with regard to the functions of the Sensory Gan- 

 glia in Man, from the facts supplied by Comparative Anatomy, by Experi- 

 mental inquiry, and by Pathological phenomena. The determination of 

 these functions may seem to be the more difficult, as it is impossible to 

 make any satisfactory experiments upon the gauglionic centres in question, 

 by isolating them completely from the Cerebral Hemispheres above, and 

 from the Medulla Oblongata and Spinal Cord below. But the evidence 

 derived from Comparative Anatomy appears to be in this case particularly 

 clear; and, rightly considered, affords us nearly all the information we re- 

 quire. In the series of " experiments prepared for us by nature," which is 

 presented to us in the descending scale of animal life, we witness the effects 

 of the gradual change in the relative development of the Sensory Ganglia 

 and Cerebral hemispheres, which are presented to us in descending through 

 the Vertebrated scale; and the results of the entire withdrawal of the latter, 

 and of the sole operation of the former, which are exhibited in the higher 

 Invertebrata (see 447, 450). ! Thus we are led by the very cogent evi- 

 dence which Comparative Anatomy supplies, to regard this series of Gangli- 

 onic centres as constituting the real Sensorium; each ganglion having the 

 power of rendering the Mind conscious of the impressions derived from the 

 organ with which it is connected. If this position be denied, we must either 

 refuse the attribute of consciousness to such animals as possess no other En- 

 cephalic centres than these; or we must believe that the addition of the 

 Cerebral hemispheres, in the Vertebrated series, alters the endowments of 

 the Sensory ganglia, an idea which is contrary to all analogy. 



524. So far as the results of Experiments can be relied on, they afford a 

 corroboration of this view. The degree in which animals high in the scale 

 of organization can perform the functions of life, without any other centres 

 of action than the Ganglia of Special sense, the Medulla Oblongata, and 

 the Cerebellum, appears extraordinary to those who are accustomed to 

 regard the Cerebral Hemispheres as the centre of all energy. From the 

 experiments of Flourens,' 2 Hertwig, 3 Mageudie, 4 Longet, 5 and others, it ap- 

 pears that not only Reptiles, but Birds and Mammals, may survive for 

 many weeks or even months (if their physical wants be duly supplied) after 

 the removal of the entire Cerebrum. It is difficult to substantiate the ex- 

 istence in them of actual wiixiitiou ; but some of their movements appear to 

 be of a higher kind than those resulting from mere excito-motor action. 

 One of the most remarkable phenomena exhibited by such a being, is the 

 power of maintaining its equilibrium, which could scarcely exist without 



1 It is worthy of special notice, that the development of the Cephalic ganglia in 

 the Invertehrata always hears an exact proportion to the development of the eyes ; 

 the other organs of special sense heing comparatively undeveloped ; whilst these, in 

 all the higher classes at least, are instruments of great perfection, and are evidently 

 connected most intimately with the direction of the movements of the animals. Of 

 this fact we have a remarkahle illustration in the history of the metamorphosis of 

 Insects ; the eyes heing almost rudimentary, and the Cephalic ganglia comparatively 

 small, in imt Larvic ; whilst lioth these organs attain a high development ill the 

 Imago, to whose actions the faculty of sight is essential. 



2 Recherches Experimentales su'r les Proprietor et les Fonctions du Systeme Ner- 

 veux, 2d edit., 1845. 



3 Kxper. de eft'ect. he-ion, in partihus Encephali, Eerol., 1820. 



4 Lr^ons sur les Fonetions du System'' Nerveux, Paris, 1839. 

 6 Traito de Physiologic, torn, ii, partie 2, I860, p. 411. 



