566 



THE NERVOUS SYSTEM 



of the superficial layers of the cerebellum, in pigeons particularly, there is 

 increasing feebleness and lack of harmony of the muscles concerned in lo- 

 comotion. When the entire organ is cut away in pigeons they lose the power of 

 walking, flying, and of standing in the usual erect way. Their power of pre- 

 serving equilibrium is lost, the most characteristic feature. Birds do not 

 remain in a state of stupor, but attempt to carry out the usual muscular activi- 

 ties. If a pigeon is laid on its back it cannot recover its erect position, though 

 it make motions to do so. If set on its feet it will fall to one side or the other, 

 and is not able to hold its head in the customary position. The endeavors of 

 the animal to maintain its balance are insecure and uncertain, resembling 

 the lack of muscular control of a drunken man. 



Such an animal does not lose the power of perceiving sensations, nor of 

 making voluntary efforts, as it will endeavor to avoid the blow that is 

 threatened. 



The experiments afford the same results when repeated on all classes of 

 animals; and from them and the others before referred to, Flourens inferred 

 that the cerebellum belongs neither to the sensory nor the intellectual ap- 

 paratus; and that it is not the source of voluntary movements, although it be- 

 longs to the motor apparatus, but is the organ for the coordination of the 

 voluntary movements, or for the excitement of the combined action of muscles. 



Such evidence as can be obtained from cases of diseases of this organ 

 confirms the view taken by Flourens; and, on the whole, it gains support from 

 comparative anatomy animals whose natural movements require most 

 frequent and exact combinations of muscular contractions being those whose 

 cerebella are most developed in proportion to the spinal cord. 



We must remember, too, that the cerebellum is connected with the posterior 

 columns of the cord through the cuneate and gracile nuclei as well as with the 

 direct cerebellar tract, all of which probably convey to the middle lobe muscular 

 sensations. It is also connected with the auditory nerves and bulb by the in- 

 ternal and external arcuate fibers; and with the tegmentum through the red 

 nuclei. Its connection with the efferent tracts from the different cerebral 

 lobes through the pons is also highly important. Movements of the eyes also 

 occur on direct stimulation of the middle lobe. It seems, therefore, to be 

 connected in some way with all of the chief sensory impulses which have to do 

 with the maintenance of the equilibrium, and is generally included in the ner- 

 vous apparatus which is supposed to govern this function of our bodies. 



Foville supposed that the cerebellum is the organ of muscular sense, i.e., the organ 

 by which the mind acquires that knowledge of the actual state and position of the muscles 

 which is essential to the exercise of the will upon them; and it must be admitted that all 

 the facts just referred to are as well explained on this hypothesis as on that of the cerebellum 

 being the organ for combining movements. A harmonious combination of muscular 

 actions must depend as much on the capability of appreciating the condition of the muscles 

 with regard to their tension, and to the force with which they are contracting, as on the 

 power which any special nerve-center may possess of exciting them to contraction. And 



