566 FUNCTIONS OF THE CEREBRO -SPINAL NERVOUS SYSTEM. 



separation between them being that which is known as the "fourth ventri- 

 cle." Interposed among the commissural fibres of the Medulla Oblongata, 

 however, are certain collections of vesicular matter, which serve as the gan- 

 glionic centres, governing the calibre of the vessels, and for the movements 

 of respiration and deglutition, the latter corresponding with the " respiratory " 

 and " stomato-gastric " ganglia of Invertebrated animals. This incorpora- 

 tion of so many distinct centres into one system, would seem destined in part 

 to afford to all of them the protection of the vertebral column ; and in part 

 to secure that consentaneousness of action and that ready means of mutual 

 influence, which are peculiarly requisite in beings in whom the activity of 

 the Nervous system is so predominant. Thus the close connection which is 

 established in the higher Vertebrated animals between the respiratory and 

 the general locomotive apparatus, is obviously subservient to the use which 

 the former makes of the latter in the performance of its functions ; whilst, on 

 the other hand, the control which their encephalic centres possess over the 

 actions of the respiratory ganglia, enables the Will to regulate the inspira- 

 tory and expiratory movements in the manner required for the acts of vocal- 

 ization. Under the term Sensory Ganglia, may be comprehended that as- 

 semblage of gauglionic masses lying along the base of the skull in Man, and 

 partly included in the Medulla Oblongata, in which the nerves of the 

 "special senses," Taste, Hearing, Sight, and Smell, have their central termi- 

 nations; and with these may probably be associated the two pairs of gangli- 

 onic bodies known as the Corpora Striata and Thalami Optici, into which 

 may be traced the greater proportion of the fibres that constitute the various 

 strands of the Medulla Oblongata, and which seem to stand in the same 

 kind of relation to the nerves of Touch or "common sensation," that the 

 Olfactive, Optic, Auditory, and Gustative ganglia bear to their several nerve- 

 trunks. 



454. Now it is not a little interesting that this Cranio-Spinal axis, which 

 represents in Vertebrated animals the whole nervous system of the Inverte- 

 brata (with the exception of the rudiment of the Sympathetic which they 

 possess), should exist in the lowest known Vertebrated animal without any su- 

 peraddition, and should be sufficient for the performance of all its actions. 

 Such is the case in the curious Amphioxus, a little fish which presents not 

 the slightest trace of either Cerebrum or Cerebellum, and in which even the 

 sensory ganglia and the organs of special sense have only a rudimentary ex- 

 istence ; and in which, too, the spinal cord is composed of a series of ganglia 

 that are obviously distinct from each other, although in close approximation. 

 And even in the lower Cyclostome' Fishes, the condition of the nervous cen- 

 tres is very little above this, save as regards the larger development of the 

 sensory ganglia. This condition has its parallel, even in the Human species, 

 in the case of Infants which are occasionally born without either Cerebrum 

 or Cerebellum ; such have existed for several hours, or even days, breathing, 

 sucking, crying, and performing various other movements ; and there is no 

 physiological reason why their lives should not be prolonged, if they be nur- 

 tured with sufficient care. 



45"). In Man, however, as in all the higher Vertebrata, we find superim- 

 posed (as it were) upon the Sensory ganglia, and constituting the principal 

 mass of the Encephalon, the bodies which are known as the Cerebral Hemis- 

 pheres, or Hemispheric (liuujlin. Now when these are so greatly developed 

 as to cover in and obscure the Sensory ganglia to the degree which presents 

 itself in Man, it is not surprising that the fundamental importance of the 

 latter should not be generally recognized; in Fishes, however, the proportion 

 between the two sets of centres is entirely reversed, the rudiments of the Cere- 



