78 THE NERVOUS SYSTEM 



ments of the thoracic walls, and many other functions the action of which 

 demands this complex sort of coordinating control. These actions of the 

 medulla are not only reflex like those of the cord farther down (i. e., 

 dependent for action on an immediately preceding nervous stimulus), 

 but to a greater degree than elsewhere (especially as concerns respiration) ; 

 the activity here is " automatic," that is, subject to stimuli not coming 

 from afar over a nerve, but acting on the central nerve-cells directly. 

 Thus, the term autochthonic is more exact and probably less misleading 

 than is "automatic," for it implies that the actuation comes from the 

 immediate environment of the cell, a theory quite in line with the most 

 advanced ideas of tissue-metabolism. In point of fact, stimuli which 

 actuate automatic centers are the physicochemical conditions of the 

 blood flowing through the gray matter of the medulla. 



Some of the medullary centers are more reflex than autochthonic. For 

 example, those of vomiting, swallowing, sneezing, coughing, sucking, 

 eye and mouth movements, as well as those centers which control the 

 secretion of sweat, saliva, and of the numerous other digestive juices 

 found within the alimentary canal, are of this reflex nature. In brute 

 animals there is also in the medulla a reflex center which actuates the 

 muscles productive of vocal sounds. Most of the centers so far named 

 produce their effects over the complicated cranial nerves. 



As essential as the foregoing functions are those which follow; they 

 too are directed by " automatically acting" medullary centers: inspira- 

 tion, expiration, cardio-inhibition, cardio-augmentation, vasoconstric- 

 tion, vasodilatation, and thermotaxis. Heubel, Nothnagel, and others 

 have called attention to a spot at the extreme upper end of the medulla 

 the chemical stimulation of which gives rise to the universal muscular 

 spasms such as are seen in the grand mal of epilepsy. What the function 

 of this arrangement of motor nerve-cells may be it is difficult to say; it 

 may be related to the thermotactic center and be concerned in regulating 

 the metabolic activity of the muscles short of their actual gross shortening 

 by contraction. Of this kind of muscular action fibrillary contraction is 

 an extreme degree. All these functions may be set in activity reflexly as 

 well as autochthonically, for these two modes in practice merge into 

 each other. All of these, besides most of the reflex centers proper, are of 

 necessity intimately connected within the gray tissue of the medulla, as, 

 indeed, a brief consideration of their interrelation in the bodily functions 

 demonstrates. 



The Cerebellum. The cerebellum is situated in man above the over- 

 hanging occipital lobes of the hemispheres and dorsal to the pons and 

 the medulla, and consists, like the hemispheres, of a rind or cortex of 

 gray matter enclosing white matter made up of nerve-fibers. As in the 

 case of the cerebral lobes, part of these fibers are engaged in associating 

 intimately all parts of the organ, while others convey impulses inward 

 to or outward from the cerebellum, connecting it most closely with the 

 great conducting organs just described that lie ventrally to it. In general 

 terms, the function of the cerebellum is to coordinate the muscular move- 



