Changes

==Testes and Epididymis==

==Testes and Epididymis==

===Scrotum===

===Scrotum===

Outer-most layer is the scrotal skin, which contains many sweat glands, thermosensitive receptors and sympathetic nerves. The ''tunica dartos'' is a smooth muscle layer found below the skin of the scrotum. In horses, this muscle forms a septum which divides the scrotal sac into right and left compartments. Smooth muscle tone is controlled by androgens released in response to temperature changes, detected by sensory nerves within the scrotal skin. The tunica dartos is responsible for holding the testes close to the body during cold temperatures, as it can maintain sustained contraction, and letting the testes lower in hot weather, increasing the surface area for heat loss from the skin. The next layer is the scrotal fascia.  

Outer-most layer is the scrotal skin, which contains many sweat glands, thermosensitive receptors and sympathetic nerves. The '''''tunica dartos''''' is a smooth muscle layer found below the skin of the scrotum. In horses, this muscle forms a septum which divides the scrotal sac into right and left compartments. Smooth muscle tone is controlled by androgens released in response to temperature changes, detected by sensory nerves within the scrotal skin. The ''tunica dartos'' is responsible for holding the testes close to the body during cold temperatures, as it can maintain sustained contraction, and letting the testes lower in hot weather, increasing the surface area for heat loss from the skin. The next layer is the scrotal fascia.  

The testes are contained within the '''tunica albiguinea''', which is a fibrous capsule composed of collagen. It also contains the testicularis arteries and veins, which are visible on the surface of the testicle.  This capsule is covered by the '''tunica vaginalis''', which is an outpocketing of the abdominal peritoneum. The tunica vaginalis can be further divided into the '''visceral and parietal tunics'''.  The visceral tunic is adherent to the testicle, ducts and vessels. The parietal tunic is continuous with the parietal peritoneum.  The parietal tunic adheres to the ''tunica dartos'' muscle, scrotal fascia and scrotal skin. The tunica albuginea sends projections from the capsules into the testicular parenchyma that join up with the mediastinum of the testis forming lobules. Contraction and relaxation of the smooth muscle fibres within the tunica albuginea in response to acetylcholine and norepinephrine results in a pumping action facilitating the flow of spermatozoa through the tubules of the testes.

The testes are contained within the '''tunica albiguinea''', which is a fibrous capsule composed of collagen. It also contains the testicularis arteries and veins, which are visible on the surface of the testicle.  This capsule is covered by the '''tunica vaginalis''', which is an outpocketing of the abdominal peritoneum. The tunica vaginalis can be further divided into the '''visceral and parietal tunics'''.  The visceral tunic is adherent to the testicle, ducts and vessels. The parietal tunic is continuous with the parietal peritoneum.  The parietal tunic adheres to the ''tunica dartos'' muscle, scrotal fascia and scrotal skin. The tunica albuginea sends projections from the capsules into the testicular parenchyma that join up with the mediastinum of the testis forming lobules. Contraction and relaxation of the smooth muscle fibres within the tunica albuginea in response to acetylcholine and norepinephrine results in a pumping action facilitating the flow of spermatozoa through the tubules of the testes.

The ''cremaster'' muscle is the caudolateral extension of the ''internal abdominal oblique'' muscle. It is continous with the parietal layer of the tunica vaginalis and inserts at the caudal pole of the testes.  

The '''''cremaster''''' muscle is the caudolateral extension of the ''internal abdominal oblique'' muscle. It is continous with the parietal layer of the tunica vaginalis and inserts at the caudal pole of the testes.  

The scrotum has important function:

The scrotum has important function: