STRUCTURE OF THE TESTIS. 481 



lies, and let it be fixed firmly in that position with pins. The fibrous coat 

 is to be cut through along the anterior part, and thrown backwards as far 

 as the entrance of the bloodvessels. Whilst raising this membrane a 

 number of fine bands will be seen traversing the substance of the testicle, 

 and a short septal piece (mediastinum) may be perceived at the back of the 

 viscus, where the vessels enter ; but it will be expedient to remove part of 

 the mass of tubes in the interior, to bring more fully into view the media- 

 stinum, and to trace back some of the finer septa to it. 



The tunica albuginea, or the fibrous coat of the testicle, is of a bluish- 

 white color, and resembles in appearance the sclerotic coat of the eyeball. 

 This membrane protects the secreting part of the testicle, and maintains 

 the shape of the organ by its dense and unyielding structure: it also sends 

 inwards processes to support and separate the seminal tubes. These seve- 

 ral offsets of the membrane appear in the dissection ; and one of them at 

 the back of the testicle, which is larger than the rest, is the mediastinum. 



The mediastinum testis (fig. 169, d) (corpus Highmorianum) projects 

 into the gland for a third of an inch with the bloodvessels. It is situate 

 at the back of the testis, extending from the upper nearly to the lower part, 

 and is rather larger and deeper above than below. It is formed of two 

 pieces, which are united anteriorly at an acute angle. To its front and 

 sides the finer septal processes are connected; and in its interior are con- 

 tained the bloodvessels behind, and a network of seminal ducts in front 

 (rete testis). 



Of \\\v finer processes of the tunica albuginea (fig. 169, b) which enter 

 the testis, there are two kinds. One set round and cord-like, but of diffe- 

 rent lengths, is attached posteriorly to the mediastinum, and serves to 

 maintain the shape of the testis. The other set forms delicate membranous 

 septa, which divide the mass of seminal tubes into lobes, and join the 

 mediastinum, like the rest. 



Within the tunica albuginea is a thin vascular layer, tunica vasculosa 

 (Sir A. Cooper), which lines the fibrous coat, covering the different septa 

 in the interior of the gland. It is formed of the ramifications of the blood- 

 vessels, united by areolar tissue, like the pia mater of the brain ; in it the 

 arteries are subdivided before they are distributed on the secerning tubes, 

 and the small veins are collected into larger trunks. 



form and length of the seminal tubes (tubuli seminiferi). The secern- 

 ing or seminal tubes are very convoluted, and are but slightly held together 

 by fine areolar tissue and surrounding bloodvessels, so that they may be 

 readily drawn out of the ttstis for some distance : their length is said by 

 Lauth to be two feet and a quarter. 



Ending, size, and structure. Within the lobes of the testis some tubes 

 end in distinct closed extremities; but the rest communicate, forming 

 loops or arches. The diameter of the tubules varies from ^J^th to T g^th 

 of an inch. The wall of the tubule is formed of a thin translucent mem- 

 brane, but it has considerable strength. Lining the interior in the child 

 is a nucleated granular epithelium, with polygonal cells; but in the adult 

 the tube is filled by cells in different stages of development of the sper- 

 matic corpuscles. On the exterior is a plexus of bloodvessels. 



Names from the arrangement of the tubes. To different parts of the 

 seminal tubes, the following names have been applied. Where the tubules 

 are collected into masses, they form the lobes of the testis. As they enter 

 the fibrous mediastinum they become straight, and are named tubuli recti. 

 Communicating in the mediastinum, they produce the rete testis. And, 

 31 



