THE PELVIS AND ITS CONTENTS. 437 
THE PELVIS. 
THE CAVITY OF THE BODY known as the pelvis is situated behind the 
abdomen, with which it communicates freely, each being lined by a con- 
tinuation of the peritoneum. A ridge of bone (the brim of the pelvis) is 
the line of demarcation anteriorly. The sacrum and os coccygis bound it 
superiorly, the anus posteriorly, and the ossa innominata inferiorly and 
laterally. It contains the bladder and rectum in both sexes, and in each 
the organs of generation peculiar to it. 
THE BLADDER. 
THE BLADDER is a musculo-membranous bag destined to contain the 
urine as it is gradually received from the ureters, which bring it down 
from the kidneys. It lies in the middle of the pelvis, occupying also 
more or less of the abdomen according to its condition in point of reple- 
tion or emptiness. It is of an oval shape, with its posterior extremity 
somewhat more pointed than the other, and called its neck. At this point 
it gives origin to the urethra, a canal for carrying off the urine. It 
receives the two ureters at its superior surface, about an inch in front of 
the neck, where they pierce the several coats in an oblique direction 
forming a complete valve, which prevents the return of the urine, and so 
invisible that the presence of two openings is scarcely ever suspected by 
the ordinary observer. Only about one-third of*the bladder is covered by 
the peritoneum, the remainder being made up solely of the muscular and 
mucous coats, which compose all the hollow viscera. It is retained in its 
place by the cellular membrane which connects it with the lower walls of 
the pelvis, posteriorly by the urethra, and by the folds of the peritoneum, 
which are continued from it to the sides of the pelvis, and are called the 
broad ligaments of the bladder. 
THE ORGANS OF GENERATION, MALE AND FEMALE. 
THE MALE ORGANS OF GENERATION consist of the testes and their ducts, 
the vasa deferentia, the latter conveying the semen to the urethra or to 
the vesicule seminales, which are oval bags connected with the upper 
surface of the neck of the bladder. Here the seminal fluid is stored up 
for use, and when wanted is conveyed into the vagina by means of the 
external organ or penis. The anatomy of the testicles is that which 
mainly concerns the horsemaster, as they are generally removed by 
operation. They are contained within the scrotum, which is externally 
composed of skin, wrinkled in the foal, but subsequently distended by the 
size and weight of its contents. Beneath this is a layer of a pale yel- 
lowish fibrous membrane called the dartos, which envelops the testes and 
forms a separation between them. <A thin coat of cellular membrane 
alone separates this from the double serous membrane, the tunica vagi- 
nalis, which almost entirely envelops each testis, just as the pleura does 
the lung. In the early stages of foetal life the testes are contained within 
the abdomen above the peritoneum, but being attached to the scrotum 
by a thin muscle (the cremaster), they are gradually dragged downwards 
through the inguinal canal; and each brings a double layer of peritoneum, 
which continues its connexion through life, so that fluid injected into the 
cavity of the tunica vaginalis will flow into the peritoneum. Hence 
inguinal hernia in the horse becomes scrotal in a very short space of time, 
