622 THE NERVOUS SYSTEM 



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 co-ordination 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 pos- 

 terior 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 internal 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. Move- 

 ments 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 nervous 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 it is because the power of such harmonious 

 movement would be equally lost, whether the injury to the cerebellum involved 

 injury to the seat of muscular sense or to the center for combining muscular 

 actions, that experiments on the subject afford no proof in one direction more 

 than the other. 



