This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The testicles begin to develop early in fetal life - about the third month - below and in front of the kidneys, opposite the second lumbar vertebra.
The testis is covered by peritoneum, which is prolonged at its upper and lower ends. The lower reaches down to the internal ring and later contains fibrous and muscular tissue and passes through the inguinal canal to the lower part of the scrotum: it is called the gubernaculum testis. It reaches its highest development in the sixth month and its remains attach the testicle to the lower part of the scrotum as the ligament of the scrotum. As the testicle descends, the upper peritoneal band covers the spermatic vessels from the region of the kidney down. The lower portion of the gubernaculum sends branches to the regions of the pubes, perineum, and saphenous opening. The testicle is preceded in its descent through the inguinal canal by a fold of peritoneum - the vaginal process - which forms the tunica vaginalis over the testicle, the part above atrophying.
The testicle may be arrested in some portion of its course, forming an undescended testicle, or it may be displaced, as Has been suggested, by an abnormal development of one of the subsidiary bands of the gubernaculum. Hence it may be found, not in the scrotum, but in the perineum, in the femoral region, or in the pubic region. It may go through the femoral canal instead of the inguinal. If it is undescended it may be arrested in the abdominal cavity, in the inguinal canal, or at the external ring.
The vaginal process may not entirely close, so that the peritoneal fluid passes down to the tunica vaginalis covering the testicle; this is called a congenital hydrocele. If the opening is large enough for intestine to enter, it forms a congenital hernia (see page 383). If the opening is closed above, usually at the external ring, and fluid accumulates in the tunica vaginalis it forms an infantile hydrocele. If a portion of the vaginal process persists somewhere along the spermatic cord between the internal ring and top of the testis it forms a cyst and is called an encysted hydrocele of the cord. The vaginal process closes at its upper portion just before birth and in those cases which are patulous after birth (congenital hernia and hydrocele) there is a tendency to spontaneous closure, hence operative measures are usually deferred. The vaginal process also descends into the inguinal canal in the female and a hydrocele of it is called a hydrocele of the canal of Nuck.
The normal testicles are 4 cm. (1 1/2 in.) long, 2.5 cm. (1 in.) wide, and 2 cm. (4/5 in.) thick. They are firm to the touch. If larger they are either hypertrophied or diseased. If hypertrophied their consistence is not materially altered, if diseased they are usually harder. If smaller they are usually atrophied and besides the lessening of size are also softer and flabby in consistency.
They lie attached at the inner posterior portion of the scrotum and their long axis points upward, slightly forward, and outward. In all cases of hernia and hydrocele the testicle is to be felt for at the inner posterior aspect of the swelling. In rare instances the testicle is placed anteriorly instead of posteriorly and is liable to be wounded in introducing a trocar into the tunica vaginalis to empty a hydrocele. To avoid this accident the position of the testicle can be determined not only by touch but also by seeing the outline of the testicle by means of a light placed on the opposite side of the scrotum. As the testicle is almost always low down the puncture should be made higher up and preferably on the outer side.