408 THE NERVOUS SYSTEM. 



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 pui> 

 pose from only a few centripetal nerves, and reflecting them 

 to the motor nerves of the same organ. The incident or cen- 

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

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

 nerve, some of the branches of the superior laryngeal nerve, 

 which are distributed to the pharynx ; and the nerves through 

 which the motor impressions to the fauces and pharynx are 

 reflected, are the pharyngeal branches of the vagus, and, in sub- 

 ordinate 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 oesophageal move- 

 ments, so far as they are connected with the medulla oblon- 

 gata, the filaments of the pneumogastric nerve alone, which 

 contain both afferent and efferent fibres, 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 

 a spinal cord is left. The movements 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 sensa- 

 tion or voluntary power. These are connected with parts next 

 to be described. 



It would appear that much of the reflecting power of the 

 medulla oblongata may be destroyed ; and yet its power in 

 the respiratory movements may remain. Thus, in patients 

 completely affected with chloroform, the winking of the eye- 

 lids ceases, and irritation of the pharynx will not produce the 

 usual movements of swallowing, or the closure of the glottis 

 (so that blood may run quietly into the stomach, or even into 

 the lungs) ; yet, with all this, they may breathe steadily, and 

 show that the power of the medulla oblougata to combine in 

 action all the nerves of the respiratory muscles is perfect. 



In addition to its influence over the functions of respiration 

 and deglutition, the medulla oblongata appears to be largely 

 concerned also in the faculty of speech. 



In the medulla oblongata appears to be seated also the 

 chief vaso-motor nerve-centre (p. 452). From this arise fibres 

 which, passing down the spinal cord, issue with the anterior 



