262 FUNCTION'S OF THE NERVOUS SYSTEM. 



enter the two coeliac ganglia, from which branches radiate to the abdominal 

 viscera. 



333. This system of ganglia and nerves has an evident affinity with the 

 Sympathetic system of Vertebrata, as well as with some parts of the Cerebro- 

 spinal system, more especially with the Par Vagum. It is to be remembered, 

 that the Pneumogastric nerve of Vertebrata is distributed to three separate 

 systems the respiratory, the circulating and the digestive. As we know 

 that the ultimate fibrils of nerves never anastomose, there can be no doubt 

 that these branches might be separately traced backwards into their ganglionic 

 centres ; and they may thus be regarded as functionally three distinct nerves, 

 though bound up in a single trunk. There is no difficulty, then, in under- 

 standing that the respiratory system of nerves, in Insects, and other In- 

 vertebrata, may be analogous with the pneumonic portion of the Par Vagum ; 

 although it bears no relation with the cardiac and gastric divisions of the 

 nerve. To the latter divisions, the analogy of the recurrent nerve becomes 

 sufficiently plain, when we look at its distribution upon the dorsal vessel, 

 cesophagus, and stomach ;* but its commencement in the anterior ganglion, 

 which also supplies the mouth and pharynx, might seem to place it on a dif- 

 ferent footing, until we have determined the true analogy of this last centre. 

 It may be inferred from its situation, and from the distribution of its nerves, 

 that this anterior ganglion is analogous both to the labial and pharyngeal 

 ganglia of the higher Mollusca. These appear to form a division of the 

 nervous system, by which the actions immediately concerned in the prehen- 

 sion of food are performed ; and these seem almost as independent of the 

 cephalic ganglia, as are those of respiration. There is evidently, however, 

 a greater tendency towards the union of these centres with the resophageal 

 collar, than of those presiding over the respiratory function, which is more 

 independent of the will. 



334. The division of the nervous system of Vertebrata with which the 

 central portion of this system corresponds, is a question of some apparent 

 difficulty; but, if we bring into comparison not only the highest but the 

 lowest forms of the cerebro-spinal apparatus, the chief difficulties will be 

 removed. The analogies drawn from the distribution of the nervous branches 

 would lead us to infer, that the third division of the Fifth pair (including its 

 sensory and motor origins), the Glosso-Pharyngeal, and the gastric portion of 

 the Par Vagum, would most nearly represent its central portion. Now, when 

 the fifth pair is traced back to its true origin, it is found to be not a cerebral 

 but a spinal nerve; and it is then seen to arise from the Medulla Oblongata, 

 in such close approximation with the par vagum and glosso-pharyngeal, as to 

 show that, if this portion of the nervous centres were isolated from the rest, 

 the nerves which proceed from it would form, anatomically as well as func- 

 tionally, a natural group. The fifth pair, like other spinal nerves, may act in 

 a simply-reflex character; although, in Man, it is usually under the dominion 

 of the will. In the lower animals we find these reflex actions bearing a much 

 larger proportion to the voluntary, than in Man; and even in him we not 

 unfrequently meet with cases, in which the functions of the cerebral hemi- 

 spheres seem suspended, whilst those of the spinal cord are unimpaired; so 

 that the prehension of food by the lips may take place without any effort of 

 the will. This lias been observed in anencephalous foatuses, in puppies from 

 which the brain has been removed, and in profound apoplexy. Further, the 

 connection between the fifth pair and par vagum is very intimate in fishes; the 

 class which approaches nearest, in the character of its nervous system, to 

 Invertebrata. We may reasonably infer, then, that the anterior ganglion is 



* See Newport, in Phil. Trans., 1832, p. 386. 



