FUNCTIONS OF THE MEDULLA OBLONGATA. 103 



Posterior Pyramids, or Corpora Pyramidalia Posteriora. (Figs. 

 27 and 28.) 



In considering the functions of these parts it is impossible to sepa- 

 rate them completely, they are so closely connected with each other, 

 and the functions of one part are so readily affected by any change 

 in those of the others. In tracing upwards the four divisions of the 

 medulla oblongata, the following are found to be their connexion 

 with the brain. 



1 . The fibres of the anterior pyramids for the most part enter the 

 crura cerebri, passing through the pons Varolii, and traversing the 

 optic thalami, (which, it must be remembered, have scarcely any 

 connexion with the optic nerves, or with the sense of sight;) after 

 which they diverge and become mingled with gray matter, thus 

 forming the corpora striata, and finally radiate to the convolutions 

 of the cerebrum. 



2. The fibres of the olivary body also pass into the pons Varolii, 

 and there divide into two bands ; one of^ which proceeds upwards 

 and forwards to join the crura cerebri, thence to pass to the optic 

 thalami ; the other passes upwards and backwards into the corpora 

 quadrigemina. 



3. The fibres of the true restiform bodies pass entirely into the 

 cerebellum. 



4. The fibres of the posterior pyramids pass directly onwards 

 through the crura cerebri into the thalami, whence they radiate to 

 the convolutions. 



The anterior pyramids may be said to connect the motor fibres 

 of the cerebral hemispheres, with the antero-lateral columns of the 

 spinal cord. Part of its fibres decussate, a large portion of those 

 that proceed from the right hemisphere passing over into the left side 

 of the cord ; and those from the left hemisphere into the right side 

 of the cord, — an arrangement which fully explains the frequent oc- 

 currence of paralytic affections on the opposite side from that affected 

 in the brain. 



The olivary bodies probably constitute the essential portion or 

 nucleus of the medulla oblongata, that on which its power as an in- 

 dependent centre depends. This opinion seems supported by the fact, 

 that these bodies and the central portion of the medulla oblongata 

 contain that intermixture of vesicular ^ndi fibrous matter which con- 

 stitutes the main character of a nervous centre. It is probably the 

 centre of the respiratory nerves. The olivary bodies are connected 

 above with the cerebral hemispheres and corpora quadrigemina, and 

 below with the antero-lateral columns of the spinal cord. 



The restiform bodies are probably associated in function with the 

 hemispheres of the cerebellum, and the posterior columns of the 

 spinal cord. 



The posterior pyramids are supposed by some to have the func- 



