OF THE NERVOUS SYSTEM. 45.0 



sisls of a central mass peculiar to that class, and composed of 

 a longitudinal cord, the spinal marrow, in which the ganglion' 

 form is no longer apparent, and whose upper or cranial extre- 

 mity, divided into the pair of cords, presents enlargements 

 and developments, which together form the encephalon. These 

 parts, viewed successively from behind forwards, are the ce- 

 rebellum, the tubercula quadrigemina, the cerebrum, properly 

 so called, and the olfactory lobes. The spinal marrow gives 

 attachment to a number of pairs of nerves corresponding to 

 that of the vertebra. Each of these nerves is furnished with 

 a ganglion near its central extremity. The cranial portion of 

 the spinal marrow (the medulla oblongata) furnishes nerves to 

 the organs of sense and the other organs of the face, and to 

 those of digestion and respiration. Moreover, there exists on 

 each side, before the vertebral column, a knotted cord (the 

 great sympathetic nerve) and nervous ganglia and cords for 

 the heart and alimentary canal, a particular nervous system, 

 which alone, or joined to the pneumo-gastric nerve, resembles 

 in its distribution the first appearances of this system in the 

 animal kingdom. 



739. The spinal marrow, which is hollow in the ovipa- 

 rous animals, becomes full in the mammifera. In the former 

 it occupies the whole length of the vertebral canal; in the 

 mammifera it extends into the sacrum. Its volume is so much 

 the greater compared with that of the brain, or the latter is so 

 much the smaller compared with the spinal marrow, as we ex- 

 amine the animal series farther removed frorTi the adult man 

 to fishes. It is cylindrical, with slight bulgings at the places 

 where the nerves of the limbs are attached to it. Its cranial 

 portion also presents enlargements in proportion to the nerves 

 there inserted. 



The cerebellum, which is formed by the posterior or resti- 

 form cords of the spinal marrow, expanded, reflected and 

 united above the fourth ventricle, is very simple in the osse- 

 ous fishes, in many of the cartilaginous fishes, and in the great- 



avec une exposition comparative de sa structure dans les animaux. Paris, 

 1823. Desmoulins; Exposition succincte du dcvdoppcment ct dcs functions 

 du systeme cerebro-spinal. 



