STRUCTURE OF THE TESTIS. 541 



The Tunica vaginalis is a pouch of serous membrane derived 

 from the peritoneum in the descent of the testis, and afterwards 

 obliterated from the abdomen to within a short distance of the gland. 

 Like other serous coverings it is a shut sac, investing the organ and 

 thence reflected so as to form a bag around its circumference ; hence 

 it is divided into the tunica vagi?ialis propria, and tunica vaginalis 

 rejlexa. The tunica vaginalis propria covers the surface of the 

 tunica albuginea, and surrounds the epididymis, connecting it to the 

 testis by means of a distinct duplicature. The tunica vaginalis re- 

 flexa is attached by its external surface, through the medium of a 

 quantity of loose cellular tissue, to the inner surface of the dartos. 

 Between the two layers is the smooth surface of the shut sac, moist- 

 ened by its proper secretion. 



The Tunica albuginea (dura mater testis) is a thick fibrous mem- 

 brane of a bluish white colour, and the proper tunic of the testicle. 

 It is adherent externally to the tunica vaginalis propria, and from 

 the union of a serous with a fibrous membrane is considered a fibro- 

 serous membrane, like the dura mater and pericardium. After sur- 

 rounding the testicle, the tunica albuginea is reflected from its pos- 

 terior border into the interior of the gland, and forms a projecting 

 longitudinal ridge, which is called the mediastinum testis (corpus 

 Highmorianum*) from which numerous fibrous cords (trabeculae, 

 septula) are given off, to be inserted into the inner surface of the 

 tunic. The mediastinum serves to contain the vessels and ducts of 

 the testicle in their passage into the substance of the organ, and the 

 fibrous cords are admirably fitted, as has been shown by Sir Astley 

 Cooper, to prevent compression of the gland. If a transverse section 

 be made of the testis, and the surface of the mediastinum examined, 

 it will be observed that the blood-vessels of the substance of the 

 organ are situated near the posterior border of the mediastinum, 

 while the divided ducts of the rete testis, occupy a place nearer to 

 the free margin. 



The Tunica vasculosa (pia mater testis) is the nutrient membrane 

 of the testis ; it is situated immediately within the tunica albuginea 

 and encloses the substance of the gland, sending processes inwards 

 between the lobules, in the same manner that the pia mater is re- 

 flected between the convolutions of the brain. 



The substance of the testis consists of numerous conical flattened 

 lobules (lobuli testis), the bases being directed towards the surface 

 of the organ, and the apices towards the mediastinum. Krause 

 found between four and five hundred of these lobules in a single 

 testis. Each lobule is invested by a distinct sheath formed by two 

 layers, one being derived from the tunica vasculosa, the other from 

 the tunica albuginea. The lobule is composed of one or several 

 minute tubuli, tubuli seminiferi,-\ exceedingly convoluted, anasto- 



* Nathaniel Highmore, a physician of Oxford, in his "Corporjs Humani Disquisitio 

 Anatomica," published in 1651 : he considers the corpus liighmorianum as a duct 

 formed by the convergence of the fibrous cords, which he mistakes for smaller ducts. 



t Lauth estimates the whole number of tubuli serniniferi in each testis, at 840, and 

 their average length at 2 feet 3 inches. According to this calculation, the whole length 

 of the tubuli scminiferi would be 1890 feet. 





