506 



THE HUMAN BODY 



This pouch is subdivided internally by a partition into right and 

 left chambers, in each of which a testicle lies. The chambers are 

 lined inside by a serous membrane, the tunica vaginalis, and this 

 doubles back (like the pleura round the lung) and covers the ex- 

 terior of the gland. Between the external and reflected layers of the 

 tunica vaginalis is a space containing a small quantity of lymph. 

 The testicles develop in the abdominal cavity, and only later 

 (though commonly before birth) descend into the scrotum, 

 passing through apertures in the muscles, etc., of the abdominal 

 wall, and then sliding down over the front of the pubes, beneath 

 the skin. The cavity of the tunica vaginalis at first is a mere 

 offshoot of the peritoneal cavity, and its 

 serous membrane is originally a part of the 

 peritoneum. In the early years of life the 

 passage along which the testis passes usually 

 becomes nearly closed up, and the com- 

 munication between the peritoneal cavity 

 and that of the tunica vaginalis is also ob- 

 literated. Traces of this passage can, how- 

 ever, readily be observed in male infants; 

 if the skin inside the thigh be tickled a 

 muscle lying beneath the skin of the scrotum 

 is made to contract reflexly, and the testis 

 is ierked up some way towards the abdo- 



FJG. 149. Diagram of J *. J , 



a vertical section through men and quite out of the scrotum. Some- 



semimferi; Cvasa Seta'; times * ne passage remains permanently open 

 d, yasa efferentia ending an( j a co ]\ o f intestine may descend along 



in the com vasculosi ; e, e, 



epididymis. h, vas def- it and enter the scrotum, constituting an 

 inguinal hernia or rupture. A hydrocele is 

 an excessive accumulation of liquid in the serous cavity of the 

 tunica vaginalis. 



Beneath its covering of serous membrane each testis has a 

 proper fibrous tunic of its own. This forms a thick mass on 

 the posterior side of the gland, from which partitions or septa 

 (i, Fig. 149) radiate, subdividing the gland into many chambers. 

 In each chamber lie several greatly coiled seminiferous tubules, a, 

 a, averaging in length 0.68 meter (27 inches) and in diameter only 

 0.14 mm. (y^ inch). Their total number in each gland is about 

 800. Near the posterior side of the testis the tubules unite to 



