ACTIONS PRELIMINARY TO DEGLUTITION. 301 



b. Comparative Anatomy supplies us with the key to the explanation of these phenomena. 

 It has been seen that, in the lower animals, the Respiratory organs are completely uncon- 

 nected with the mouth, and that a very distinct set of muscles is provided to keep them in 

 action. These muscles have distinct ganglia as the centres of their operations ; and these 

 ganglia are only connected indirectly with those of the sensori-motor system. The same 

 would appear to be the case, in regard to the introduction of the food into the digestive 

 apparatus. It has been shown that the muscles concerned in this operation have their own 

 centres. the Stomato-gastric and Pharyngeal ganglia, which are not very closely connected 

 with the cephalic, or with the respiratory, or with those of general locomotion. Now in the 

 Vertebrata, the distinct organs have been so far blended together, that the same muscles 

 serve the purposes of both; but the different sets of movements of these muscles are excited 

 by different nerves; and the effect of division of either nerve, is to throw the muscle out of 

 connection with the function, to which that nerve previously rendered it subservient, as 

 much as if the muscle were separated from the nervous system altogether. There is an 

 apparent exception to this view of the matter, in the case of the Portio Dura; this being the 

 source of those movements of the upper lip, which, in many animals, are essential to the 

 prehension of food. These movements, however, are dependent upon sensations conveyed 

 through the Fifth pair.* being completely checked by division of its infra-orbital trunk; and 

 it can scarcely be doubted, from their general character, that they are of a strictly voluntary 

 nature, and are not to be regarded as part of the reflex associated movements in which that 

 nerve is concerned. 



c. Now although, in the adult Human being, the movements required to convey the food 

 to the pharynx are under the control of the Will, if not constantly dependent upon it, there 

 is good reason to believe that this is not the case in regard to those remarkable associated 

 movements, which constitute the act of suction in the Infant. The experiments provided 

 for us by nature, in the production of anencephalous monstrosities, fully prove that the 

 nervous connection of the lips and respiratory organs with the Spinal Cord, is alone sufficient 

 for its execution; and Mr. Grainger has sufficiently established the same, by experiment 

 upon puppies whose brain had been removed. He adds that, as one of the puppies lay on 

 its side, sucking the finger which was presented to it, it pushed out its feet in the same 

 manner as young pigs exert theirs against the sow's dugs. On the whole, however, the act 

 of suction belongs more to the Respiratory ganglion (so to speak) than to the Stomato-gastric 

 system of nerves; and hence we can understand why, even in the highest animals, it should 

 be purely reflex; the movements of Respiration being so from the first, whilst those ordi- 

 narily concerned at a later period in the Ingestion of the food are more directed by sensa- 

 tion and volition. The actions of the mammary foetus of the kangaroo, described by Mr. 

 Morgan, furnish a very interesting exemplification of the same function of the Spinal Cord ; 

 this creature, resembling an earth-worm in appearance, and only about fourteen lines in 

 length, with a brain corresponding in degree of development to that of a human fcetus of 

 the ninth week, executes regular, but slow, movements of respiration, adheres firmly to the 

 point of the nipple, and moves its limbs when disturbed. The milk is forced into the oeso- 

 phagus by a compressor muscle, with which the mamma of the parent is provided. . " Can it 

 be imagined," very justly asks Mr. Grainger, '-that in this case there are sensation and vo- 

 lition, in what can be proved anatomically to be a fostus?" 



387. The Sphincter muscle, which guards the Cardiac orifice of the 

 stomach, appears to be under the influence of the Spinal system of nerves. 

 It is usually closed; but it opens when there is a sufficient pressure on it, 

 made by the accumulated food propelled by the movements of the oesophagus 

 above ; and it then closes again, so as to retain the food in the stomach. 

 That this closure is due to reflex action appears from the fact that, when the 

 nerves supplying the muscle are divided, the sphincter no longer contracts, 

 and the food regurgitates into the oesophagus. The opening of the cardiac 

 orifice is one of the first of the changes, which occur in the act of vomiting. 

 With regard to the degree, in which the movements of the Stomach, that have 

 so important a share in the Digestive operation, are dependent upon the Spinal 

 system, and are consequently of a reflex nature, it is difficult to speak with 



* Hence originated one of Sir C. Bell's early errors. He found that an ass, in which the 

 infra-orbital branch of the fifth was divided, would not pick up oats with its lip, although 

 they were in contact with it; hence he concluded that its power of motion was destroyed, 

 when it was in reality only the sensation necessary to excite the will to cause the motion, 

 that was deficient. 



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