STRUCTURE AND FUNCTIONS OF THE MEDULLA OBLONGATA. 507 



afferent portion of the Fifth pair is also a powerful excitor ; and the 

 afferent portions of all the spinal nerves, conveying impressions from 

 the general surface of the body, are also capable of contributing to the 

 excitement necessary for the production of the movement. The chief 

 motor nerves are the phrenic and intercostals ; which, though issuing 

 from the Cord at a considerable space lower down, probably originate 

 in the Medulla Oblongata. The motor portions of several other spinal 

 nerves are also partly concerned ; as are also the Facial nerve, the 

 motor portion of the Par Yagum, and the Spinal Accessory. The 

 ordinary movements of Respiration involve little action of any motor 

 nerves but the Phrenic and Intercostal ; and it is only when an excess 

 of the stimulus (produced, for example, by too long a suspension of the 

 aerating process) excites extraordinary movements, that the nerves last 

 enumerated are called into action. 



806. The acts of Prehension of food with lips, and of Mastication, 

 though usually effected by voluntary power in the adult, seem to be 

 capable of taking place as a part of the reflex operation of the Medulla 

 Oblongata, in the Infant, as in the lower animals. This is particularly 

 evident in the prehension of the nipple by the lips of the infant, and 

 the act of suction which the contact of that body (or of any resembling 

 it) seems to excite. The experiments provided for us by nature, in the 

 production of anencephalous monstrosities, fully prove that the integrity 

 of the nervous connexion of the lips and respiratory organs with the 

 Medulla Oblongata, is alone sufficient for the performance of this action; 

 and experiments upon young animals, from which the brain has been 

 removed, establish the same fact. Thus Mr. Grainger found that, upon 

 introducing his finger, moistened with milk, or with sugar and water, 

 between the lips of a puppy thus mutilated, the act of suction was 

 excited ; and not merely the act of suction itself, but other movements 

 having a relation to it ; for as the puppy lay on its side, sucking the 

 finger, it pushed out its feet, in the same manner as young pigs exert 

 theirs in compressing the sow's dugs. This action seems akin to many 

 of those, by which the lower animals take in their food; and we may 

 thus recognise in the Medulla Oblongata a distinct centre of reflex 

 action for the reception and deglutition of aliment, analogous to the 

 stomato-gastric ganglia of Invertebrated animals. 



897. In the movements of Deglutition, which, as formerly explained 

 ( 453), are purely reflex, the chief excitor is undoubtedly the afferent 

 portion of the Glosso-pharyngeal nerve. It is found that, if the trunk of 

 this nerve, or its pharyngeal (but not its lingual) branches, be pinched, 

 pricked, or otherwise irritated, whilst still in connexion with the Medulla 

 Oblongata, the movements concerned in the act of swallowing are 

 excited. The same occurs if, when the trunk of the Glosso-pharyn- 

 geal has been divided, the cut extremity in connexion with the Medulla 

 Oblongata is irritated; but little or no muscular contraction is produced 

 by irritation of the separated extremity ; whence it is apparent, that 

 the Glosso-pharyngeal has little or no direct motor power, but acts as 

 an excitor. In this it appears to be assisted by the branches of the 

 Fifth pair distributed upon the fauces ; and probably, also, by the 

 branches of the superior laryngeal distributed upon the Pharynx. The 



