5i8 THE NERVOUS SYSTEM. 



the act of deglutition (see p. 271). This is proved by the 

 persistence of the power of swallowing after destruction 

 of the cerebral hemispheres and cerebellum ; its existence 

 in anencephalous monsters ; the power of swallowing pos- 

 sessed by marsupial embryoes before the brain is developed ; 

 and by the complete arrest of the power of swallowing 

 when the medulla oblongata is injured in experiments. 

 But the reflecting power herein exercised by the medulla 

 oblongata is of a much simpler and more restricted kind 

 than that exercised in respiration ; it is, indeed, not more 

 than a simple instance of reflex action by a segment of the 

 spinal axis, receiving impressions for this purpose from 

 only a few centripetal nerves, and reflecting them to the 

 motor nerves of the same organ. The incident or centri- 

 petal nerves in this case are the branches of the glosso- 

 pharyngeal, and, in a subordinate degree, those of the 

 cervical nerves, which combine to form the pharyngeal 

 plexus ; and the nerves through which the motor impres- 

 sions to the fauces and pharynx are reflected, are the 

 pharyngeal branches of the vagus, and, in subordinate 

 degrees, or as supplying muscles accessory to the move- 

 ments of the pharynx, the branches of the hypoglossal, 

 facial, cervical, recurrent, and fifth nerves. For the 

 cesophageal movements, so far as they are connected with 

 the medulla oblongata, the filaments of the pneumogastric 

 nerve alone appear to be sufficient (John Reid). 



Though respiration and life continue while the medulla 

 oblongata is perfect and in connection with respiratory 

 nerves, yet, when all the brain above it is removed, there 

 is no more appearance of sensation, or will, or of any 

 mental act in the animal, the subject of the experiment, 

 than there is when only the spinal cord is left. The move- 

 ments are all involuntary and unfelt;. and the medulla 

 oblongata has, therefore, no claim to be considered as an 

 organ of the mind, or as the seat of sensation or volun- 

 tary power. These are connected with parts next to be 

 described. 



