604 STRUCTURE OF THE TESTIS. 



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 of a quantity of loose areolar tis- 

 sue, 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 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 surrounding 

 the testicle, 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 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 shewn by Sir Astley Cooper, to prevent com- 

 pression 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 mater is reflected 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 of 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, anastomosing frequently 

 with each other near their extremities, terminating in loops or in free 

 caecal ends, and of the same diameter (-^^ of an inch, Lauth) through- 

 out. The tubuli seminiferi are of a bright yellow colour ; they become 

 less convoluted in the apices of the lobules, and terminate by forming 

 between twenty and thirty small straight ducts of about twice the dia- 



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

 Disquisitio Anatomica," published in 1651, considers the corpus Highmo- 

 rianum 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 seminiferi in each testis at 

 840. and their average length at 2 feet 3 inches. According to this calculation, 

 the whole length of the tubuli seminiferi would be 18QO feet. 



