posterior part will be seen to be reflected over the body of the gland
as the tunica albuginea, while the anterior part blends with the
cellular tissue of the front wall of the scrotum. The tunica vaginalis,
6 d, is now traceable as a distinct sac,[Footnote] closed on all sides,
and reflected from the fore part of the testicle, above and below, to
the posterior aspect of the front wall of the scrotum.

[Footnote: Mr. Owen states that the Chimpanzee alone, amongst brute
animals, has the tunica vaginalis as a distinct sac.]

[Illustration: Abdomen and scrotum, showing bone, blood vessels
and other internal organs.]
Plate 39--Figure 3

PLATE 40, Fig. 1.--The abdomino-scrotal serous lining remains continuous
at the internal ring, and a congenital hydrocele is formed.--When the
serous spermatic tube, 6 b, 6 c, remains pervious and continuous above
with the peritonaeum, 6 a, and below with the serous tunica vaginalis, 6
d, the serous fluid of the abdomen will naturally gravitate to the most
depending part--viz., the tunica vaginalis; and thus a hydrocele is
formed. This kind of hydrocele is named congenital, owing to the
circumstance that the natural process of obliteration, by which the
peritonaeum becomes separated from the tunica vaginalis, has been, from
some cause, arrested. [Footnote 1] As long as the canal of
communication, 6 b, 6 c, between the tunica vaginalis, 6 d, and the
peritonaeum 6 a, remains pervious, which it may be throughout life, this
form of hydrocele is, of course, liable to occur. It may be diagnosed
from diseased enlargements of the testicle, by its transparency, its
fluctuation, and its smooth, uniform fulness and shape, besides its
being of less weight than a diseased testis of the same size would be.
It may be distinguished from the common form of hydrocele of the
isolated tunica vaginalis by the fact, that pressure made on the scrotum
will cause the fluid to pass freely into the general cavity of the
peritonaeum. As the fluid distends the tunica vaginalis, 6 c, 6 d, in
front of the testis, this organ will of course lie towards the back of
the scrotum, and therefore, if it be found necessary to evacuate the
fluid, the puncture may be made with most safety in front of the
scrotum. If ascites should form in an adult in whom the tunica vaginalis
still communicates with the peritonaeal sac, the fluid which accumulates
in the latter membrane will also distend the former, and all the
collected f