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Male reproductive system (organa genitalia masculina) 297

Until it is joined by the ductus deferens, the urethra ernosum or vasculare). The extent of the vascular stratum
VetBooks.ir exclusively carries urine (pars praeprostatica). Beyond this varies considerably. In the penile urethra it becomes mark-
point, it assumes the additional function of transporting edly enlarged, forming the corpus spongiosum penis. The
innermost cavernous spaces are small, becoming larger
semen.
The urethra is a musculomembranous tube (Figures towards the periphery. The caverns are particularly promi-
13.32 to 13.34). Longitudinal mucosal folds are evident nent in the stallion.
throughout its length. These are lost during ejaculation The tunica muscularis begins at the neck of the bladder
and urination. Most of the urethra is lined with transi- as a three-layered muscular mantle. It continues as striated
tional epithelium. Isolated regions of simple stratified muscle (outer and inner layer of the m. urethralis). The
columnar epithelium may be present. Near the glans penis circularly oriented fibres form a complete layer in the stal-
or processus urethrae the mucosal lining transforms into lion, carnivore and billy goat. In the bull, boar and ram
stratified squamous epithelium. the dorsal component of this layer is missing. The tunica
In the pelvic urethra, the lamina propria is composed muscularis is surrounded by a tunica adventitia which
of fibro-elastic tissue containing smooth muscle cells and, radiates into the capsule of the penis.
in some cases, lymphocytic infiltrates. Mucous tubular
glands (glandulae urethrales) are present in the stallion Penis
and tomcat. At the end of the pelvic portion, the lamina The penis consists of the body (corpus penis) with its
propria contains numerous thin-walled veins (caverns) paired erectile bodies (corpora cavernosa penis), and the
that form a subepithelial vascular stratum (stratum cav- urethra and its associated unpaired erectile tissue (corpus

13.32 Cross-section of penis at the level of the glans (dog). Haematoxylin and eosin stain (x7).

13.33 Cross-section of penis (stallion). Haematoxylin and eosin stain (x5).

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