1006 THE DIGESTIVE SYSTEM. 
which are particularly well developed, afford, by their simultaneous contraction, an effective 
means of closing the cesophagus immediately above the eardia, and thus of preventing regurgita- 
tion of the contents of the stomach. 
The pyloric orifice or pylorus is the aperture through which the stomach com- 
municates with the duodenum. It is marked on the surface by a shght constriction, 
most evident at the curvatures; and in the interior by a prominent thickening of 
the wall—the pyloric valve (valvula pylori)—produced by a special dev elopment of 
the cireular muscular fibres, known as the pyloric sphincter (musculus sphincter 
pylori). When examined post-mortem in the ordinary way, the aperture, viewed 
from the duodenal side, is somewhat oval in form, and closely resembles the external 
os uteri (Cunningham). When seen from the opposite side, it presents an irregular 
or stellate appearance, owing to the fact that the rug of the gastric mucous 
membrane are continued up to the orifice. . 
The pylorus rests on the neck of the pancreas below and behind, and is over- 
lapped by the liver above and in front. Its average position can be marked on the 
surface of the body by the intersection of two lines; one drawn horizontally half- 
way between the top of the sternum and the pubie crest (Addison), the other ‘drawn 
vertically a little way (4 inch, 12 mm.) to the right of the middle line. 
During the earlier stages of gastric digestion the sphincter pylori is strongly contracted 
and the aperture firmly closed, but it opens intermittently to allow of the passage of properly 
digested portions of the food. "As digestion advances the sphincter probably relaxes somewhat ; 
but in hardened bodies a really patent pylorus is rarely or never found, which would seem to 
indicate that the pylorus is normally closed, or nearly so, and that its opening is an active rather 
than a passive condition, as in the case of the anal canal. 
As regards its size, the pylorus is stated to be about $ inch (125 mm.) in diameter, but there 
is no doubt that this represents neither its full size nor the calibre of the valve when at rest. 
Foreign bodies with a diameter of #? 
to 1 inch have been known to pass 
through the pylorus without giving 
rise to trouble, even in children. On 
the other hand, when at rest, with an 
empty stomach and duodenum, the 
aperture, as seen in formalin-hardened 
hodies, is practically closed, and pre- 
sents a stellate or purse-mouth appear- 
ance, viewed from either aspect. In 
hardened bodies with distended stomach 
and duodenum, the aperture, which is 
somewhat oval, is practically closed, and 
Faleiform 
— ligament (eut) 
Liver 
(enlarged) —~ 
Pyloric end of 
/ —— stomach 
Tenth rib Subcostal line 
Gall- 
bladder Great from the duodenal side resembles the 
omentum . . 
Transverse ; external os uteri. But both in the 
colon empty and the distended condition of 
Descending 
the stomach the pylorus seems to be 
poROn of colon 
umbilicus rather a tubular ee extending 
‘mall over at least $ to 1 inch of the « anal, 
poet =a eons than a sudden constriction. 
pa When the stomach is empty the 
pylorus is usually placed near (ve. 
within } inch, 12 mm. of) the middle 
line, beneath the left or sometimes the 
quadrate lobe of the liver, and at the 
. ; level of the first lumbar vertebra, or 
| 7 | the dise between this and the second 
lumbar. During distension it is pushed 
i) 1 2 3 4 5 0 5 10 
ean 
SCALE JN INCHES SCALE IN CENTIMETRES 
Fic. 678.— ABDOMEN OF FEMALE, SHOWING DISPLACEMENTS 
RESULTING FROM TIGHT LACING. 
The liver is much enlarged, and extends on the left side to 
the ribs, where it was folded back on itself for over an 
inch. The pyloric end of the stomach and the beginning 
of the duodenum are quite superficial below the liver, and 
all the viscera are displaced downwards. (From a photo- 
graph of a body hardened by injections of formalin. ) 
over beneath the quadrate lobe for a 
variable distance, but very rarely more 
than 1} or 2 inches to the right of the 
middle line; and its orifice, instead 
of looking towards the right, is then 
directed backwards, for, as already ex- 
plained, the antrum in distension is 
carried to the right in front of the 
pylorus, or even beyond it. 
Peritoneal Relations. — The 
stomach is almost completely covered by peritoneum—the anterior surface being 
clothed by the posterior layer of the great sac, and the posterior surface by the 
