PREHENSION OF FOOD. 561 



of M. Magendie, 1 that when the cerebrum and a great part of the cere- 

 bellum were removed in ducks, the instinct of seeking food was lost in 

 every instance, and the instinct of deglutition in many : food, however, 

 introduced into the stomach, was found to be digested. 



b. Prehension of Food. 



The arms and mouth have been described as organs of prehension. 

 It is scarcely necessary to say, that the hands seize the food and convey 

 it to the mouth under ordinary circumstances; but there are cases in 

 which the mouth is the sole-or chief organ of prehension. Most animals 

 are compelled to use the mouth only. When the food is conveyed to it 

 by the hands, it must open to receive it. The mode in which this is 

 effected has given rise to controversy; and, strange to say, is not yet 

 considered determined. Whilst some physiologists have asserted, that 

 the lower jaw alone acts in opening the mouth moderately; others have 

 affirmed, -that both the jaws separate a little; the lower, however, 

 moving five or six times as much as the upper. That the latter is the 

 correct view can be proved by positive experiment. If, when the mouth 

 is closed, we place the flat side of the blade of a knife against the teeth 

 of both jaws; and, holding the knife immovably, separate the jaws; we 

 find, that both jaws move on the blade; but the lower to a much greater 

 extent than the upper. Now, as the upper jaw is fixed immovably to 

 the head, the whole head must, of necessity, participate in this move- 

 ment; and the question arises, what are the agents that produce it? 

 Some attribute it to a slight action of the extensor muscles of the head; 

 and affirm, that whilst the depressors of the lower jaw carry it down- 

 wards, the extensors of the head draw the head slightly backwards, and 

 thus raise the upper jaw. 



MM. Magendie 2 and Adelon 3 assert, that when the mouth is opened 

 moderately, the upper jaw does not participate; but, that if the motion 

 be "forced" or extensive, it participates slightly. The experiment, 

 however, with the knife, which is adduced by M. Adelon himself, com- 

 pletely overthrows this notion; and shows, that both jaws act, whenever 

 the mouth is slightly opened. M. Magendie agrees with those who con- 

 sider, that, whenever the upper jaw is raised, it must be by the head 

 being thrown back on the vertebral column ; and he properly remarks, 

 that where there is a physical impediment to the depression of the lower 

 jaw, the mouth must be opened solely by the retroversion of the head 

 on the spine. M. Ferrein 4 conceived, that the motion of the upper jaw is 

 occasioned by the action of the stylo-hyoideus muscle, and the posterior 

 belly of the digastricus; and he affirms, that whilst the anterior fasci- 

 culus or belly of the digastricus depresses the lower jaw; the posterior 

 belly with the stylo-hyoideus carries the head backwards, and, with it, 

 the upper jaw. The attachments, however, of these muscles sufficiently 

 show, that they cannot be the agents : the mastoid process, to which 

 the posterior belly of the digastric muscle is attached, is near the arti- 

 culation of the head with the atlas; whilst the styloid process, to which 



1 Precis, &c., ii. 168. 2 Op. citat., ii. 43. 3 Op. citat., ii. 408. 



4 Memoir, de 1'Acad. des Sciences pour 1744. 



VOL. i. 36 



