646 OF THE FUNCTIONS OF THE NERVOUS SYSTEM. 



its interior; and each segmental division of it, which serves as the centre for- 

 its own pair of nerves, may be considered, like each ganglion of the ventral 

 column of the Articulata, as a repetition of the single "pedal" or locomotive 

 ganglion of the Mollusca. The Medulla Oblongata consists of a set of strands, 

 which essentially correspond with the cords that pass round the oesophagus in 

 Invertebrated animals, connecting the cephalic ganglia with the first sub-cesopha- 

 geal ganglion ; but, as the whole cranio-spinal axis in the Vertebrata lies above 

 the alimentary canal (the trunk being supposed to be in a horizontal position), 

 there is no such divergence of these strands, the only separation between them 

 being that which is known as the " fourth ventricle/' Interposed among the 

 commissural fibres of the Medulla Oblongata, however, are certain collections of 

 vesicular matter, which serve as the ganglionic centres for the movements of 

 respiration and deglutition, and which thus correspond with the respiratory and 

 stomato-gastric ganglia of Invertebrated animals. This incorporation 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 con- 

 sentaneousness 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 appa- 

 ratus, 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 inspiratory and expiratory movements in the 

 manner required for the acts of vocalization. Under the term Sensory Ganglia 

 may be comprehended that assemblage of ganglionic 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 terminations ; and with these may probably be associated the two pairs 

 of ganglionic 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. 



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

 represents in Vertebrated animals the whole nervous system of the Invertebrata 

 (with the exception of the rudiment of the Sympathetic which they possess), 

 should exist in the lowest known Vertebrated animal without any superaddi- 

 tion, and should be sufficient for the performance of all its actions. Such is the 

 case in the curious Amphioxus* 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 existence ; 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 Cyclos- 

 tome Fishes, the condition of the nervous centres 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 occa- 

 sionally 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 nurtured with sufficient care ( 373). 



1 "Princ. of Phys. Gen. and Comp.," \ 321, Am. Ed. 



