196 ANATOMY OF THE RABBIT. 
3. The urinary bladder (vesica urinaria) lies in the ventral 
posterior portion of the abdominal cavity. It is a muscular sac, 
capable of a considerable amount of distension, but usually found 
in preserved animals ina greatly contracted condition. Its rounded 
anterior end, the vertex, projects forward into the abdominal 
cavity, while its posterior portion or fundus, narrows to.a canal, 
the urethra, which receives on its dorsal wall the apertures of the 
genital ducts and those of the related glands. The connections 
may be made out as follows: 
(a) The peritoneum is reflected from the ventral surface of the 
rectum in the male and from the uterus in the female, to the 
bladder, and after investing the latter passes to the ventral 
abdominal wall. The dorsal peritoneum forms in the male 
a double rectovesical fold (plica rectovesicalis), and in the 
female a similar vesicouterine fold, a recess of considerable 
extent (rectovesical or vesicouterine pouch) being left 
becween the adjacent structures. 
The ventral peritoneum forms a broad median vertical 
sheet, the middle umbilical fold (plica umbilicalis media). 
The free edge of this fold, extending from the vertex of the 
bladder to the umbilicus, contains a slender cord, the middle 
umbilical ligament (lig. umbilicale medium). The latter 
marks the position of the peripheral portions of the um- 
bilical arteries in the foetus. 
(b) The umbilical artery (a. umbilicalis), a branch of the hypo- 
gastric, passes along the side of the bladder to the vertex. 
From the base of the artery branches are given off to the 
ureter (a. urecerica) and related portions of the genital ducts, 
B. The Male Genital Organs. , 
I. Continue the median ventral incision of the skin backward 
along the symphysis to the penis. Reflect the skin on both sides 
to clear the attachments of the penis to the ischium, and on the left 
to a point beyond the scrotum. Note the cremaster muscle 
(m. cremaster), a thin layer of muscle fibres forming the outer 
layer of the sac of the testis. It is continuous with the internal 
oblique muscle of the abdominal wall, and also contains fibres 
