n8 THE POCKET ANATOMY 



THE MEDULLA OBLONGATA, OR BULB. 



Extent. From the lower border of the foramen magnum to 

 the lower border of the pons Varolii. 



Connections. Inferiorly it is connected with the spinal cord, 

 superiorly it is continued into the pons, anteriorly it rests 

 upon the basilar groove, and posteriorly it lies in a depression 

 between the hemispheres of the cerebellum, called the valle- 

 cula, and here bounds the lower half of the floor of the 4th 

 ventricle. 



Dimensions. 1 inches long ; greatest breadth f inch. 



Shape. Pyramidal, with base at the pons, and apex at the 

 spinal cord. 



Fissures. Anterior and posterior median fissures, con- 

 tinuous with those of the cord. 



Anterior median fissure: terminates just below the pons in 

 the foramen cfscum. The fibres of the anterior pyramids decus- 

 sate at the lower part of the fissure, and partly interrupt it. 



Posterior median fissure : continues up from the cord to about 

 half-way up the medulla, where it widens out into the fossa 

 rhomboidalis or floor of the 4th ventricle. 



Structure of the medulla. If the parts of the spinal cord 

 are traced into the medulla, its structure will be easily under- 

 stood. 



The line of the posterior roots of the spinal nerves is continued 

 by the upper bundles of the nerve-roots of the spinal acces- 

 sory nerve, above this by the bundles of the vagus, and 

 above this, again, by the bundles of the glosso-pharyngeal 

 nerve. 



The line of exit of these nerve-roots represents the postero- 

 lateral groove of the spinal cord. As this line is traced up- 

 wards it turns ventrally outwards, so that about half-way up 

 the medulla it appears upon the lateral surface, and in its 

 upper part it lies close to the posterior margin of the olivary 

 body, from which it is separated by a narrow groove. 



The part behind these nerve-roots is termed the posterior 

 area of the medulla, and corresponds to the posterior columns 

 (postero-mesial and postero-lateral) of the cord. 



The line of the anterior roots of the spinal nerves, when 

 traced up into the medulla, deepens into a groove which is 

 continued upwards nearly as far as the pons. 



The bundles of the nerve-roots of the hypoglossal issue 

 from this groove. The part of the medulla between this 

 groove and the anterior median fissure is called the anterior 

 area, and corresponds to the anterior column of the cord. 



