AREAS OF THE MEDULLA OBLONGATA 



871 



ventricle. This involves a tilting of the functionally differentiated gray segments 

 and, after a gradual transition in the medulla oblongata, the motor gray is to be 



Corpora 

 quadrigemina 



Ependymal 



lining 

 of ventricle 



Fourth 

 ventricle 



Inferior 

 medullary velum 



Choroid plexus 

 terna basalis of subarachnoid space 



Central canal 



Cisterna pontis of 

 subarachnoid space 



FIG. 635. Scheme of roof of fourth ventricle. 



sought nearest the middle line, 

 the mixed gray just ectad, while 

 the sensor is the outermost of all. 

 Instead of the ventral, lateral, 

 and dorsal horns of each half of 

 the spinal cord, we have an ental, 

 middle, and ectal cornu in each 

 half of the medulla oblongata. 

 The positions alone have changed ; 

 the functional relations to nerve 

 roots having corresponding func- 

 tions are homologous. Thus, 

 the motor hypoglossal nucleus is 

 placed in the mesal part of the 

 ventricular floor, while the termi- 

 nal nuclei of the afferent vagus, 

 glossopharyngeal, and auditory 

 nerves lie in the lateral part. 



Another cardinal change in the 

 internal structure of the medulla 

 oblongata, accompanying the pre- 

 ponderating development of the 

 cerebrum and great basal gan- 

 glia, is caused by interrupting and 

 decussating fibre systems which 

 seek passage through the brain 

 stem and encroach more or less 

 on its primitive architecture. 

 While in the spinal cord there is a perfect continuity of the central tubular gray, we 

 find in the medulla oblongata more pronounced peninsular and isolated insular 

 nuclei or ganglionic gray masses. 



PYRAMIDAL 



DECUSSATION 



CROSSED PYRAMIDAL 

 TRACT 



DIRECT PYRAMIDAL 

 TRACT 



FIG. 636. Schema of the pyramidal decussation 



