B. The external iliac artery, cut across. C. The upper part of the rectum. D. The ascending pubic ramus. E. The spine of the ischium, cut. F. The horizontal pubic ramus, cut. G. The summit of the bladder covered by the peritonaeum; G *, its side, not covered by the membrane. H H. The recto-vesical peritonaeal pouch, I. The vas deferens. K. The ureter. L. The vesicula seminalis. M, N, O, P, Q, R, S, T, U, refer to the same parts as in Plate 48. V. The prostate. W. The lower part of the rectum. X. The deep perinaeal fascia. [Illustration: Abdomen, showing bone, blood vessels and other internal organs.] Plate 49 COMMENTARY ON PLATES 50 & 51. THE SURGICAL DISSECTION OF THE SUPERFICIAL STRUCTURES OF THE MALE PERINAEUM. The median line of the body is marked as the situation where the opposite halves unite and constitute a perfect symmetrical figure. Every structure--superficial as well as deep--which occupies the median line is either single, by the union of halves, or dual, by the cleavage and partition of halves. The two sides of the body being absolutely similar, the median line at which they unite is therefore common to both. Union along the median line is an occlusion taking place by the junction of sides; and every hiatus or opening, whether normal or abnormal, which happens at this line, signifies an omission in the process of central union. The sexual peculiarities are the results of the operation of this law, and all forms which are anomalous to either sex, may be interpreted as gradations in the same process of development; a few of these latter occasionally come under the notice of the surgeon.