CEREBELLUM, PONS, AND MEDULLA. 245 



which take account of the true genetic relations of the various 

 lobes and lobules of the cerebellum, and they have been rewarded 

 by obtaining results of a positive character. The newer anatomical 

 nomenclature is illustrated in Fig. 105, which gives a schematic 

 representation of the arrangement of the lobules of the cere- 

 bellum of the dog, according to Bolk. Following this schema 

 van Rynberk reports that excision of the lobulus simplex is 

 followed by movements of the head (head nystagmus), which 

 indicate an abnormal innervation of the neck muscles. Injury 

 on one side of the crus primum of the ansiform lobule is followed 

 by abnormal movements of the forefoot of the same side, while 

 similar injuries to the crus secundum result in abnormal move- 

 ments localized to the hind foot. Extirpation of a lobulus 

 paramedianus causes rolling movements round the long axis 

 of the body or bending of the body to one side (pleurothotonus). 

 These experimental results have been confirmed in part by obser- 

 vations on clinical cases in which the asynergy following cere- 

 bellar lesions showed some indication of a localization to one or 

 another part of the body. 



The Medulla Oblongata. In the medulla oblongata we must 

 recognize a region of special physiological importance in that it 

 is the seat of certain centers which control the activity of the 

 circulatory and respiratory organs. If the medulla is severed 

 from the portion of the brain lying anterior to it the animal con- 

 tinues to live for a considerable period. The respiratory move- 

 ments are performed rhythmically, and the blood-vessels retain 

 their tone so as to maintain an approximately normal blood-pressure. 

 On the contrary, destruction of the medulla, or severance of its 

 connections with the underlying parts, is followed by a cessation 

 of respiration and a loss of tone in the arteries, either of which 

 results in the rapid death of the organism as a whole. The portions 

 of the medulla which exercise these important functions are desig- 

 nated, respectively, as the respiratory and the vasomotor or vaso- 

 constrictor centers. Their location and to some extent their con- 

 nections have been determined by physiological experiments, but 

 so far it has not been possible to mark out histologically the exact 

 groups of cells concerned. The position and physiological properties 

 of these centers are described in the sections on respiration and 

 circulation. These centers are of especial importance because of 

 their wide connections with the body, their essentially independent 

 activity in reference to the higher parts of the brain, and the abso- 

 lutely necessary character of the regulations they effect. In the 

 development of the brain the functions originally mediated by the 

 lower parts have been transferred more and more to the higher 

 parts, especially in regard to conscious sensation and motion, and 



