THE TESTES AND THEIR COVERINGS 



the spermatic vessels enter the gland. It is applied to the tunica vasculosa over 

 the glandular substance of the testis, and, at its posterior border, is reflected 

 into the interior of the gland, forming an incomplete vertical septum, called the 

 mediastinum testis (corpus Highmori) . 



The mediastinum testis extends from the upper to near the lower extremity 

 of the gland, and is wider above than below. From its front and sides numerous 

 imperfect septa (trabeculce) are given off, which radiate toward the surface of the 

 organ, and are attached to the tunica albuginea. They divide the interior of the 

 organ into a number of incomplete spaces which are somewhat cone-shaped, being 

 broad at their bases at the surface of the gland, and becoming narrower as they 

 converge to the mediastinum. The mediastinum supports the vessels and duct 

 of the testis in their passage to and from the substance of the gland. 



The Tunica Vasculosa is the vascular layer of the testis, consisting of a plexus 

 of bloodvessels, held together by delicate areolar tissue. It clothes the inner sur- 

 face of the tunica albuginea and the different septa in the interior of the gland, 

 and therefore forms an internal investment to all the spaces of which the gland is 

 composed. 



Structure. The glandular structure of the testis consists of numerous lobules. Their number, 

 in a single testis, is estimated by Berres at 250, and by Krause at 400. They differ in size 

 according to their position, those in the middle of the gland being larger and longer. The 

 lobules (Fig. 1149) are conical in shape, the base being directed toward the circumference of the 

 organ, the apex toward the mediastinum. Each lobule 

 is contained in one of the intervals between the fibrous 

 septa which extend between the mediastinum testis 

 and the tunica albuginea, and consists of from one to 

 three, or more, minute convoluted tubes, the tubuli 

 seminif eri. The tubules may be separately unravelled, 

 by careful dissection under water, and may be seen to 

 commence either by free cecal ends or by anastomotic 

 loops. They are supported by loose connective tissue 

 which contains here and there groups of "interstitial 

 cells" containing yellow pigment granules. The total 

 number of tubules is estimated by Lauth at 840, and 

 the average length of each is 70 to 80 cm. Their diam- 

 eter varies from 0.12 to 0.3 mm. The tubules are pale 

 in color in early life, but in old age they acquire a deep 

 yellow tinge from containing much fatty matter. Each 

 tubule consists of a basement layer formed of lamin- 

 ated connective tissue containing numerous elastic fibers 

 with flattened cells between the layers and covered ex- 

 ternally by a layer of flattened epithelioid cells. Within 

 the basement membrane are epithelial cells arranged 

 in several irregular layers, which are not always clearly 

 separated, but which may be arranged in three different 

 groups (Fig. 1150). Among these cells may be seen the 

 spermatozoa in different stages of development. (1) 

 Lining the basement membrane and forming the outer 

 zone is a layer of cubical cells, with small nuclei; 

 some of these enlarge to become spermatogonia. The 

 nuclei of some of the spermatogonia may be seen to be in process of indirect division (karyo- 

 kineses, page 37) , and in consequence of this daughter cells are formed, which constitute the second 

 zone. (2) Within this first layer is to be seen a number of larger polyhedral cells, with clear 

 nuclei, arranged in two or three layers; these are the intermediate cells or spermatocytes. Most 

 of these cells are in a condition of karyokinetic division, and the cells which result from this 

 division form those of the next layer, the spermatoblasts or spermatids. (3) The third layer of 

 cells consists of the spermatoblasts or spermatids, and each of these, without further subdivision, 

 becomes a spermatozoon. The spermatids are small polyhedral cells, the nucleus of each of 

 which contains half the usual number of chromosomes. In addition to these three layers of cells 

 others are seen, which are termed the supporting cells (cells of Sertoli). They are elongated 

 and columnar, and project inward from the basement membrane toward the lumen of the tube. 

 As development of the spermatozoa proceeds the latter group themselves around the inner 

 extremities of the supporting cells. The nuclear portion of the spermatid, which is partly 



Tunica vagimdis 

 Tunica albuginea 

 Its septa 



FIG. 1149. Vertical section of the testis, to 

 show the arrangement of the ducts. 



