Henry Gray (18251861). Anatomy of the Human Body. 1918.
imbedded in the supporting cell, is differentiated to form the head of the spermatozoön, while part of the cell protoplasm forms the middle piece and the tail is produced by an outgrowth from the double centriole of the cell. Ultimately the heads are liberated and the spermatozoa are set free. The structure of the spermatozoa is described on pages 42, 43.
In the apices of the lobules, the tubules become less convoluted, assume a nearly straight course, and unite together to form from twenty to thirty larger ducts, of about 0.5 mm. in diameter, and these, from their straight course, are called tubuli recti(Fig. 1149).
FIG. 1150 Transverse section of a tubule of the testis of a rat. X 250. (See enlarged image)
The tubuli recti enter the fibrous tissue of the mediastinum, and pass upward and backward, forming, in their ascent, a close net-work of anastomosing tubes which are merely channels in the fibrous stroma, lined by flattened epithelium, and having no proper walls; this constitutes the rete testis. At the upper end of the mediastinum, the vessels of the rete testis terminate in from twelve to fifteen or twenty ducts, the ductuli efferentes; they perforate the tunica albuginea, and carry the seminal fluid from the testis to the epididymis. Their course is at first straight; they then become enlarged, and exceedingly convoluted, and form a series of conical masses, the coni vasculosi, which together constitute the head of the epididymis. Each cone consists of a single convoluted duct, from 15 to 20 cm. in length, the diameter of which gradually decreases from the testis to the epididymis. Opposite the bases of the cones the efferent vessels open at narrow intervals into a single duct, which constitutes, by its complex convolutions, the body and tail of the epididymis. When the convolutions of this tube are unravelled, it measures upward of 6 meters in length; it increases in diameter and thickness as it approaches the ductus deferens. The convolutions are held together by fine areolar tissue, and by bands of fibrous tissue.
The tubuli recti have very thin walls; like the channels of the rete testis they are lined by a single layer of flattened epithelium. The ductuli efferentes and the tube of the epididymis have walls of considerable thickness, on account of the presence in them of muscular tissue, which is principally arranged in a circular manner. These tubes are lined by columnar ciliated epithelium (Fig. 1151).