HUMAN TESTIS AND EPIDIDYMIS 



395 



epithelium, and the branches run more or less parallel to the sur- 

 face, as described by Allen; the second and third sets are given off 

 respectivel}' nearer the mediastinum. Beyond the third set of 

 branches the cords grow centripetally without further branching. 

 The figure or pattern thus produced, which is given in a very 

 much simplified and idealized form in figure 1, results apparently 

 from the fact that the testis cords possess a normal rate of branch- 

 ing, and are moreover limited in length by the thickness of the 

 genital ridge. Three, or possibly four, sets of branches, a certain 

 distance apart, are all that each cord produces. 



Fig. 1 Diagram of testis network of human embryo of 20 mm. Outer dotted 

 line represents germinal epithelium, solid lines represent testis cords. 



The cords forming this network vary in diameter, and, though 

 usually approximately round, in certain places they are flattened, 

 forming plate-like structures, often where three or four cords join. 

 Sometimes these plates are pierced, making larger or smaller 

 rings. 



This network is completed shortly after the cords have become 

 detached from the peritoneal epithelium, and before the central 

 tips have joined the rete cords; in the human embryo this corre- 

 sponds to a length of about 20 mm. to 22 mm. Further growth 

 takes place in two ways; by the increase in diameter of the cords, 

 and by the increase in thickness of the genital ridge, caused by the 

 lengthening of the radially disposed cords, not at their ends, but 

 throughout their whole extent, so that the cross connections are 



