During the embryonic fetal life the testes descend from their original position (at 10th thoracic level) to their final location in the scrotum. During the 7th week of development a mesenchymal condensation, called gubernaculum testis is formed below the testis on each side. This mesenchymal condensation, which appears like a ligamentous cord, is composed of mucoid extracellular matrix containing a few stellate cells. The superior end of the gubernaculum attaches to the lower pole of the developing testis, while its inferior end grows caudally in the posterior abdominal wall and then around the pelvic brim to reach the inguinal region. Here it grows in caudomedial direction between the developing external and internal oblique muscles, thus creating a provisional inguinal canal. Finally the inferior end of the gubernaculum attaches to the internal surface of the labioscrotal swelling.
The descent of testes occurs in two phases. The first phase occurs between the 8th and 12th weeks. At the end of this phase the testes come to lie in the vicinity of the deep inguinal rings. This early downward movement of the testes is thought to result from the shortening of the gubernacula. As each gubernaculum shortens, its extraabdominal portion becomes gradually thicker. This thickening serves the
additional purpose of enlarging the in- essus vaginalis and bulges forward into
guinal canal. its cavity. The connection between the
The testes remain in the vicinity peritoneal cavity and the expanded of the deep inguinal ring for about three lower end of the processus becomes month. The second phase of descent obliterated just before or shortly after of testes begins in the 7th month. The birth. The lower portion of the proces-testes pass through the inguinal canal sus persists as an isolated peritoneal during the 8th month and come to rest sac called tunica vaginalis, which con-in the scrotum in the 9th month of intra- sists of visceral and parietal layers. The uterine life. The second phase of testi- visceral layer of the tunica vaginalis is cular descent is the result of actual re- applied closely to the anterior and lat-gression of the gubernaculum as a re- eral surfaces of the testis, whereas the suit of loss of the mucoid extracellular remainder of the peritoneal sac that matrix that forms major component of covers the internal surface of the scro-its substance. The migration of the tes- turn constitutes the parietal layer of the tis through the inguinal canal is also tunica vaginalis. The lumen of the tu-aided by the increased intra-abdominal . nica vaginalis is normally collapsed but pressure produced by the rapid growth under pathological conditions its may of the abdominal (viscera. The process become filled with fluid, forming a tes-is also influenced by testosterone and ticular hydrocele. other antirogens produced by the inter- As the testis and ductus defer-stitial cells of the developing testes. ens descend, they become ensheathed The action of anti-Mullerian hormone by the fascial extensions of the anterior (produced by the Sertoli cells) also abdominal wall: (i) the extension of the seems to be important for the second transversalis fascia becomes the inter-phase of testicular descent. The gu- nal spermatic fascia, (ii) the extension bernaculum persists as a tiny band of of the internal oblique muscle becomes fibrous tissue attaching the inferior pole cremasteric muscle and cremasteric of the testis to the scrotum in the neo- fascia, and (iii) extension of the nate. aponeurosis of the external oblique
During the 6th month an evagi- muscle constitutes the external sper-
nation of the peritoneum, called pro- matic fascia.
cessus vaginalis, develops ventral to The ductus deferens, blood ves-the gubernaculum and herniates into sels and lymphatic vessels of the testis the scrotum through the path formed by are carried down into the scrotum the gubernaculum. The testis descends along with the testis. They are embed-through the inguinal canal posterior to ded in connective tissue and constitute the processus vaginalis. Finally, when the spermatic cord. Owing to the path the testis reaches the scrotum, it lies taken by the testis during descent, the posterior to the distal part of the proc- ductus deferens loops over the ureter.
As the testis migrates interiorly, testicular lymphatic and blood vessels grow actively to enable the testis to descend into the scrotum. However, these vessels retain their initial origins and terminations high up on the posterior abdominal wall. Consequently, the tes-ticular arteries are branches of the abdominal aorta; the right testicular vein drains into the inferior vena cava; the left testicular vein drains into the left renal vein; and the testicular lymphatics drain into the para-aortic lymph nodes.