constructed the anterior parietes of the abdomen of yielding material.
The muscular parietes of the abdomen relax during every inspiration, and
thus this cavity gains that space which it loses by the encroachment of
the dilating lungs.

The mechanical principle upon which the abdominal chamber is
constructed, enables it to adjust its capacity to such exigence or
pressing necessity as its own visceral organs impose on it, from time to
time; and the relation which the abdominal cavity bears to the thoracic
chamber, enables it also to be compensatory to this latter. When the
inspiratory thorax gains space from the abdomen, or when space is
demanded for the increasing bulk of the alimentary canal, or for the
enlarging pregnant uterus; or when, in consequence of disease, such as
dropsical accumulation, more room is wanted, then the abdominal chamber
supplies the demand by the anterior bulge or swell of its expansile
muscular parietes.

The position of the heart itself is affected by the expansion of the
lungs on either side of it. As the expanding lungs force the diaphragm
downwards, the heart follows it, and all the abdominal viscera yield
place to the descending thoracic contents. In strong muscular efforts
the diaphragm plays an important part, for, previously to making forced
efforts, the lungs are distended with air, so as to swell and render
fixed the thoracic walls into which so many powerful muscles of the
shoulders, the neck, back, and abdomen, are inserted; at the same time
the muscular diaphragm L L*, becomes tense and unbent from its arched
form, thereby contracting abdominal space, which now has no compensation
for this loss of space, since the abdominal parietes are also rendered
firm and unyielding. It is at this crisis of muscular effort that the
abdominal viscera become impacted together; and, acting by their own
elasticity against the muscular force, make an exit for themselves
through the weakest parts of the abdominal walls, and thus herniae of
various kinds are produced. The most common situations of abdominal
herniae are at the inguinal regions, towards which the intestines, T T,
naturally gravitate; and at these situations the abdominal parietes are
weak and membranous.

The contents of a hernial protrusion through the abdominal parietes,
correspond in general with those divisions of the intestinal tube, which
naturally lie adjacent to the part where the rupture has taken place. In
the umbilical h