GENERAL ANATOMY OF THE MAMMALIAN BODY 
15 
which passes posteriorly to the external orifice within the uro¬ 
genital sinus. 
In the male note that the testes are located ventral, i.e., 
external, to the pubic arch, where they lie in the scrotal sacs, a 
position which they have reached by descending from the abdomi¬ 
nal cavity through the inguinal canal (cf. the condition found in 
some young males, before this descent has occurred). Note that 
in this descent the testis has carried with it (1) certain muscul&r 
elements from the abdominal wall, forming the cremasteric 
muscle surrounding the testis within the scrotal sac, (2) a double 
layer of peritoneum, the outer derived from the parietal perito¬ 
neum in the inguinal region, the inner consisting of the reduplica- 
ture known as the mesorchium, in which the testis and its 
associated structures lie. Note the course of the ductus deferens 
anteriorly through the inguinal canal forming (together with the 
spermatic nerve, artery and vein), the spermatic cord; its dorsal 
and posterior course within the abdominal and pelvic cavities 
to reach the dorsal surface of the urethra into which it opens; the 
seminal vesicle, often very voluminous, which opens into the ure¬ 
thra in association with the ductus deferentia; accessory glands 
(increasing the liquid portion of the seminal fluid), consisting 
mainly of the prostate gland located at the junction of the two 
ductus deferentia, and the bulbourethral gland lying along the 
dorsal urethral wall; the penis, the distal portion of which is 
usually withdrawn within a reduplicature of skin known as the 
prepuce. 
Before finally discarding the specimen, remove the kidneys 
with a short length of the ureters attached and preserve in 5% 
formalin or in 70% alcohol for later study. 
D. THE PLAN OF THE BODY AS SHOWN IN TRANS¬ 
VERSE SECTIONS AND IN A MEDIAN SAGITTAL 
. SECTION. 
For the general plan of any vertebrate body, study a trans¬ 
verse section through the middle of the body (ccelomic region) of 
a dogfish, in which the relationships are less complicated than in 
the mammals. For camparison, study demonstration prepara¬ 
tions made by sawing through the frozen bodies of adult mammals, 
