30 LECTUEES ON THE CENTRAL NERVOUS SYSTEM. 



pass through these parts. Through the presence of all these 

 structures this portion of the brain is thicker than the spinal 

 cord, which comes next to it. The latter forms a column from 

 the segments of which there arise anteriorly the motor and 

 posteriorly the sensory nerves. The space to the outside of the 

 nuclei of the nerves is occupied by fibres which connect the 

 spinal cord with the brain, and the different portions of the 

 spinal cord with one another. 



In the oblongata and spinal cord of certain animals we find peculiar 

 structures, which have resulted from hypertrophy of some pre-existing organ. I 

 will only mention, as examples, the great hypertrophy of the motor nucleus of 

 the trigeminal in the ray, the lobus electricus ; the enormous nucleus of the 

 vagus of fishes, projecting high into the fourth ventricle, which, together with 

 the trigeminal, provides for the sensation of the skin ; and the hypertrophy of 

 the posterior horns of the spinal cord in certain fishes (Trigla). 



