818 PHYSIOLOGY OP THE DOMESTIC ANIMALS. 



operation. The method by which this influence on the liberation of 

 sugar by the liver is accomplished has been described under the heading 

 of Glycogenesis. 



2. The Course of the Fibres op the Medulla Oblongata. — We 

 have now to attempt to trace the paths of communication of the different 

 divisions of the medulla oblongata with the cerebrum, pons varolii, cor- 

 pora quadrigemina, and, still more important than all, the formation of 

 the hemispheres of the cerebrum and their means of communication by 

 the cerebral peduncles with the mid-brain and its ganglia and with the 

 cerebellum. 



In tracing up the fibres from the medulla, those most readily followed 

 are the continuations of the restiform bodies, which may be readily 

 detected to pass directly into the cerebellum. Their termination after 

 reaching the cerebellum is only partially cleared up, and before attempt- 

 ing its explanation we must first consider the mode of construction of 

 the cerebellum itself. 



The cerebellum consists, in the domestic animals and man, of two 

 flattened hemispheres connected across the middle line by the middle 

 lobe or vermiform appendix, which is the fundamental portion of the 

 organ. The white substance of the cerebellum exceeds to a considerable 

 degree the gray matter. The latter is deposited over the entire surface 

 of the two hemispheres of the cerebellum, forming the gray cortex of the 

 cerebellum ; within the inner white medullary substance of the hemisphere 

 is a collection of gray matter known as the dentate or ciliary body, 

 which in its general appearance somewhat resembles that of the olivary 

 bodies found in the medulla oblongata, and which here, also, has the 

 shape of a horseshoe, thrown up into numerous folds, and near which are 

 also found associate nuclei. Although it is clearly established that the 

 main function of the gray matter is to bring the nerve-fibres and nerve- 

 cells into connection with each other, still, as yet, no direct termination 

 of nerve-tubes in the ganglion cells of the cerebellum has been detected. 

 Of course, this does not impby that the terminations of the gray cells in 

 the cortex of the cerebellum with nerve-cylinders may not be readily 

 determined. All attempts, however, to follow up these nerve-fibres has 

 as yet resulted in almost total failure. If, however, we follow the resti- 

 form bodies (which form the inferior peduncles of the cerebellum) it may 

 be seen that a certain amount of their fibres decussates and then enters into 

 the dentate body, forming the so-called intra-ciliary fibres, while another 

 passes externally and forms the extra-ciliary column. 



In addition to its communication with the medulla, the cerebellum is 

 likewise in communication with the corpora quadrigemina and the pons 

 varolii. The fibres passing from the cerebellum to the corpora quadri- 

 gemina and crura cerebri (superior cerebellar peduncles) originate not 



