542 STRUCTURE OF THE TEST1S. 



in which fat is never deposited, but which is very susceptible of serous 

 infiltration. 



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 vaginalis propria^ and tunica vaginalis refleza. The tunica vagi- 

 nalis 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 reflexa is attached by its external surface, through 

 the medium oT a quantity of loose areolar tissue, to the inner surface of the 

 dartos. Between the two layers is the smooth surface of the shut sac, 

 moistened by its proper secretion. 



The Tunica albuginea (dura mater testis) is a thick fibrous membrane, 

 of a bluish white colour, and the proper tunic of the testicle. It is adhe- 

 rent externally to the tunica vaginalis propria, and from the union of a 

 serous with a fibrous membrane is considered to be a fibro-serous mem- 

 brane, like the dura mater and Dericardium. After surrounding the tes- 

 ticle, the tunica albuginea is reflected from its posterior border into the 

 interior of the gland, and forms a projecting longitudinal ridge, which is 

 called the mediastinum testis (corpus Highmorianum*), from which nume- 

 rous fibrous cords (trabecula?, 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 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 inater is reflected between the convolu- 

 tions 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 of two layers, one being derived from the 

 tunica vasculosa, the other from the tunica albuginea. The lobule is com- 

 posed of one or several minute tubuli, tubuli seminiferi^ exceedingly con- 

 voluted, anastomosing frequently with each other near their extremities, 

 terminating in loops or in free csecal ends, and of the same diameter 



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

 Anatomica," published in 1651, considers the corpus Highmorianum as a duct formed 

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



j- i^auth estimates the whole number of tubuli seminiferi in each testis at 840, and 

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

 pf the tubuli seminiferi would be 1890 feet. 



