closely attached to the inner surface of the chest walls and mesially to
the outer layer of the pericardium; above it is thickened by a fibrous
contribution from the scalene muscles, and this forms the _dome of the
pleura_ which fits into the concavity of the first rib and contains the
apex of the lung. The reflection of the serous layer of the pleura, from
the parietal to the visceral part, takes place at the root of the lung,
where the great vessels enter, and continues for some distance below
this as the _ligamentum latum pulmonis_. The upper limit of the pleural
cavity reaches about half an inch above the inner third of the clavicle,
while, below, it may be marked out by a line drawn from the twelfth
thoracic spine to the tenth rib in the mid axillary line, the eighth rib
in the nipple line, and the sixth rib at its junction with the sternum.
There is probably very little difference in the lower level of the
pleurae on the two sides.

[Illustration: FIG. 1.--Diagram of vertical median section of Abdomen.

A, Aorta. D, Duodenum.
P, Pancreas. B, Bladder.
I, Intestine. St, Stomach.
R, Rectum. C, Colon.
L, Liver. V, Vagina.

(The fine dots represent the great sac of the peritoneum, the coarse
dots the lesser sac.)]

The _peritoneum_ is a more extensive and complicated membrane than
either the pericardium or pleura; it surrounds the abdominal and pelvic
viscera, and, like the other sacs, has a parietal and visceral layer.
The line of reflection of these, though a continuous one, is very
tortuous. The peritoneum consists of a _greater_ and _lesser sac_ which
communicate through an opening known as the _foramen of Winslow_, and
the most satisfactory way of understanding these is to follow the
reflections first in a vertical median (sagittal) section and then in a
horizontal one, the body being supposed to be in the upright position.
If a median sagittal section be studied first, and a start be made at
the umbilicus (see fig. 1), the parietal peritoneum is seen to run
upward, lining the anterior abdominal wall, and then to pass along the
under surface of the diaphragm till its posterior third is reached; here
there is a reflection on to the liver (L), forming the anterior layer of
the _coronary ligament_ of that viscus, while the membrane now becomes
visceral and envelops the front of the liver as far back as the
transverse fissure on its lower surface; here it is reflect