276 A Manual of Veterinary Physiology. 



than those of the cord. The inferior spinal columns form 

 the inferior pyramids of the medulla, the superior form the 

 superior pyramids, and the lateral columns dividing into 

 three parts help to form the restiform bodies. 



As each of the main paths or highways in the cord are 

 either going to or coming from the brain, it is interesting 

 to briefly understand their distribution. 



The pyramidal tract of the cord divides in the medulla 

 into three paths ; one proceeding to the motor areas in the 

 cerebrum, one to the cerebrum itself, and one to the corpora 

 quadrigemina. The cerebellar tract of the cord passes 

 through the medulla, and so reaches the cerebellum. The 

 antero-lateral columns run also to the cerebellum, whilst 

 the superior column of the spinal cord divides in the 

 medulla into three paths, two to the cerebellum, and one to 

 the cerebrum ; in this way each pathway in the spinal cord 

 finds either an origin or termination in the brain. 



The grey matter of the cord does not maintain its charac- 

 teristic appearance in the medulla ; owing to the decus- 

 sation of fibres in the inferior pyramid the grey and white 

 matter get mingled up, and nuclei and masses of nerve 

 cells are formed as the result. From these nuclei nearly 

 all the cranial nerves arise. 



The various tracts passing through the medulla are com- 

 posed of motor and sensory nerves, or, more correctly, 

 afferent and efferent nerves ; both of these decussate in the 

 medulla. But, in addition to these, we have reflex and 

 other centres so numerous and widespread, that it is 

 remarkable how the varied functions carried out by them 

 can be performed within such a limited area. 



The decussation of the motor tracts, as previously men- 

 tioned, causes a right, brain lesion to produce a left body 

 paralysis ; and as the sensory fibres decussate in the cord, 

 as described when speaking of the spinal cord, insensibility 

 of the left limbs would result from injury or disease of the 

 right brain (see Fig. 26). 



Centres in the Medulla. — The various centres found in the 

 medulla are of such importance to Life thai an injury to 



