DIGESTION OF FOOD. 835 
and of the vagus. The efferent nerves are those of the numer- 
ous muscles concerned. 
When food has reached the gullet, it is, of course, no longer 
under the control of the will. 
Section of the vagus or stimulation of this nerve modifies 
the action of the cesophagus, though it is known that contrac- 
tions may be excited in the excised organ; but no doubt nor- 
mally the movements of the gullet arise in response to natural 
nerve stimulation. 
Comparative.—That swallowing is independent of gravity is 
evident from the fact that long-necked animals (horse, giraffe) 
can and do usually swallow with the head and neck down, so 
that the fluid is rolled up an inclined plane. The peristaltic 
nature of the contractions of the gullet can also be well seen 
in such animals. In the frog the gullet, as well as the mouth, 
is lined with ciliated epithelium, so that in a recently killed 
animal one may watch a slice of moistened cork disappear from 
the mouth, to be found shortly afterward in the stomach. The 
rate of the descent is surprising—in fact, the movement is 
plainly visible to the unaided eye. 
The Movements of the Stomach.—The stomach of mammals, 
including man, is provided with three layers of muscular fibers: 
1. External longitudinal, a continuation of those of the cesopha- 
gus. 2. Middle circular. 3. Internal oblique. The latter are 
Fia. 282.Human stomach (after Sappey). 1, cesophagus ; 2, circular fibers at cesophageal 
opening ; 3, 3, circular fibers at lesser curvature ; 4, 4, circular fibers at the pylorus ; 5, 5, 
6, 7, 8, oblique fibers ; 9, 10, fibers of this layer covering the greater pouch ; 11, portion of 
stomach from which these fibers have been removed to show the subjacent circular fibers. 
