378 



FUNCTIONS OF THE NERVOUS SYSTEM. 



Afferent and Motor Nerves 

 of Respiration, Deglutition, 

 &e. 



Respiratory and 

 Stomato-gastric Ganglia, 

 in Medulla Oblonsata. 



Afferent and Motor Nerves 

 of Respiration, Deglutition, 

 '&c. 



Trunks of Spinal nerves, composed of 

 afferent and motor fibres from true 

 Spinal Cord and Medulla Oblongata ; 

 and probably also of sensory and 

 motor fibres, connected by the longi- 

 tudinal strands of the Cord, with the 

 Sensory Ganglia. 



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Trunks of Spinal Nerves, composed of 

 afferent and motor fibres from true 

 Spinal Cord and Medulla Oblongata ; 

 and probably also of sensory and 

 motor fibres, connected by the longi- 

 tudinal strands of the Cord, with the 

 Sensory Ganglia. 



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The Spinal Cord, the Medulla Oblongata, and Sensory Ganglia, seem to 

 constitute one continuous group of ganglionic centres ; which must be regarded 

 as the fundamental portion of the Nervous System. In descending the Verte- 

 brated series, we find the Cerebrum and Cerebellum gradually diminishing in 

 size and importance, and at last, in the .flmphioxits, disappearing altogether ; 

 and the Cranio-Spinal axis, which then remains, differs in nothing but the 

 continuity of its vesicular structure, from the nervous system characteristic of 

 the Articulata, in which the vesicular matter is broken up (so to speak) into 

 distinct centres. In this Cranio-Spinal Axis, all the nerves have their termi- 

 nation ; and, from what has been ascertained of the anatomy of the gangliated 

 cord in the Articulata, there seems much reason to believe, that their fibres 

 may pass, in the longitudinal strands of the Cord, to great distances from their 

 points of entrance or emersion ; so that we may have, in the nerves connected 

 with every part of the Cord, sensory fibres, whose real termination is in the 

 Sensory ganglia at its summit, and motor fibres, which originate from these 

 centres, and are the instruments of all the actions to which they minister. 

 The great difficulty of tracing the individual fibres of the Spinal Cord, for any 

 considerable part of its length, renders it impossible, however, to say with 

 certainty that this is their real disposition ; but it is known that one at least 

 of the nerves, the Third pair, has this double connection with the Sensory 

 Ganglia and the Spinal Cord (or rather the Medulla Oblongata), and it is 

 likely that the same is true of the other motor nerves of the Orbit. Hence 

 there is no improbability in the idea, that of the afferent fibres of the Spinal 

 nerves, some are connected with the vesicular matter of the part of the Spinal 

 Cord through which they pass, and others with the Sensory Ganglia in the 

 Encephalon ; the relative numbers entering these centres being accordant with 

 the chief purposes of the trunk, whether as an excitor of reflex actions, or as 

 destined to arouse sensations: and that the like is true of the motor fibres, 

 the relative proportions of those derived from the two sources having reference 

 to the character of the motions, whether simply-reflex or consensual, to 

 which the trunk is destined to minister. But there is by no means the same 

 evidence, that any fibres contained in the nerves actually go on to the Cere- 

 brum and the Cerebellum; and the probability seems rather, that the fibres 

 which connect these masses with the Cranio-spinal Axis are of a commissural 



