COMPARATIVE ANATOMY AND PHYSIOLOGY. 115 



lie the second pair, which are in connection with them. Two cords pass 

 backwards on each side, one derived from the anterior, the other from the 

 posterior, of these ganglia. They run along the sides of the oesophagus and 

 dorsal vessel; and, after inosculating with the branches of the central system, 

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

 viscera. 



151. 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 anastomoze, 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 understanding 

 that the respiratory system of Insects and other Invertebrata 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, oesophagus, and stomach ;* but its 

 commencement in the anterior ganglion, which also supplies the mouth and 

 pharynx, might seem to place it on a different footing, until we have deter- 

 mined the true analogy of this last centre. It may be inferred from its situa- 

 tion, 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 prehension of food are performed ; and these 

 seem almost as independent of the cephalic ganglia as are those of respira- 

 tion. There is evidently, however, a greater tendency towards the union of 

 these centres with the cesophageal collar than of those presiding over the 

 respiratory function, which is more independent of the will. 



152. The division of the nervous system of Vertebrata with which this 

 Stomato-Gastric system corresponds, is a question of more 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 ana- 

 logies 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 it. 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 ner- 

 vous centres were isolated from the rest, the nerves which proceed from it 

 would form, anatomically, as well as functionally, 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 hemispheres 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 has been observed in anen- 

 cephalous foetuses, in puppies from which the brain has been removed, and 

 in profound apoplexy. Further, the connection between the Fifth pair and 



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



