602 



PHYSIOLOGY OF THE BRAIN-STEM 



2. THE MEDULLA OBLONGATA, OR AFTERBRAIN 



The medulla oblongata extends from the upper end of the spinal cord to 

 the lower edge of the pons, its upper border being just a little dorsal to the 

 lateral recess of the fourth ventricle. Its length on the ventral side is from 

 20 to 24 mm. and on the dorsal from 24 to 26 mm. 



The physiological significance of the medulla consists chiefly in this,, that 

 within its borders the afferent and efferent pathways of the cord are brought 



FIG. 268. Transverse section of the medulla oblongata, after Edinger. 



into much more intimate relationships with each other and with the cranial 

 nerves and pathways than is the case in the cord itself. By this means the 

 efferent nerves from the cord can act together for a common purpose in a 

 much more orderly manner than would be possible on the basis of their 

 connections in the spinal cord alone, a thing of profound importance for the 

 unity of the bodily functions. 



The centers which exemplify this influence of the medulla in the highest 

 degree are the vasomotor and respiratory centers., the physiological purpose 

 and mode of action of which have been discussed at pages 237 and 325. 

 Vomiting may also be mentioned as an instance of coordination of many 

 different muscles to a common end, the center for which is probably situated 

 also in the medulla (cf. page 286). 



It is very probable that the centers for several other general functions, which, 

 like vasodilatation, require the harmonious action of many different spinal nerves, 

 lie in the medulla; experimental proof of their presence, however, is wanting at 

 this time. 



