PLATE 40, Fig. 3.--Hydrocele of the isolated tunica vaginalis.--When the serous spermatic tube, 6 b, 6 c, becomes obliterated, according to the normal rule, after the descent of the testicle, 7, the tunica vaginalis, 6 d, is then a distinct serous sac. If a hydrocele form in this sac, it may be distinguished from the congenital variety by its remaining undiminished in bulk when the subject assumes the horizontal position, or when pressure is made on the tumour, for its contents cannot now be forced into the abdomen. The testicle, 7, holds the same position in this as it does in the congenital hydrocele. [Footnote] The radical cure may be performed here without endangering the peritonaeal sac. Congenital hydrocele is of a cylindrical shape; and this is mentioned as distinguishing it from isolated hydrocele of the tunica vaginalis, which is pyriform; but this mark will fail when the cord is at the same time distended, as it may be, in the latter form of the complaint. [Footnote: When a hydrocele is interposed between the eye and a strong light, the testis appears as an opaque body at the back of the tunica vaginalis. But this position of the organ is, from several causes, liable to vary. The testis may have become morbidly adherent to the front wall of the serous sac, in which case the hydrocele will distend the sac laterally. Or the testis may be so transposed in the scrotum, that, whilst the gland occupies its front part, the distended tunica vaginalis is turned behind. The tunica vaginalis, like the serous spermatic tube, may, in consequence of inflammatory fibrinous effusion, become sacculated-multilocular, in which case, if a hydrocele form, the position of the testis will vary accordingly.--See Sir Astley Cooper's work, ("Anatomy and Diseases of the Testis;") Morton's "Surgical Anatomy;" Mr. Curling's "Treatise on Diseases of the Testis;" and also his article "Testicle," in the Cyclopaedia of Anatomy and Physiology.] [Illustration: Abdomen and scrotum, showing bone, blood vessels and other internal organs.] Plate 40--Figure 3.