In Plate VIII. the line marked † is the antero posterior diameter of the _upper strait_, through which the child first passes, called also the brim, or entrance to the Pelvis. The line marked ‡ is the diameter of the _lower_ strait, through which the child passes into the world, called also the outlet of the Pelvis. In Plate VII. the line marked † crosses the upper strait, or brim of the Pelvis. _The diameters of the Pelvis_ are the distances between the prominent points of each strait, and are four in number for each, _those for the upper_ strait being represented below. PLATE IX. _Diameters of the Upper Strait._ A B, which extends from the most prominent point of the Sacrum, to the top of the Symphysis pubes, is called the _antero posterior_ diameter, or that from before to behind.--C D, and E F, are called the two _oblique diameters_; they extend from each sacro iliac symphysis, to the most prominent point of the Os Ilium on the opposite side.--G H, is called the Transverse, or _bis iliac_ diameter, it crosses the Pelvis nearly from one hip joint to the other. The Sacro Antero posterior diameter measures _four inches_. The two oblique diameters _four inches and a half_ each. The bis iliac diameter measures _five inches_. (By comparing this with Plate VII. the various points will be still more apparent.) The inferior strait has also four diameters, represented in Plate X. [Illustration: Plate IX. Diameters of the Upper Strait.] PLATE X. The Bones of the Pelvis viewed from below, looking through the inferior strait, to show its diameters. A B, which extends from the end of the Coccygis to the lower part of the Symphysis Pubis, is called the _antero posterior_ diameter; it measures _four inches_, like that of the upper strait, but is increased a little by the bending back of the Coccygis.--C D, and E F, are the two _oblique diameters_, also corresponding to those in the upper strait; they measure _four inches_, but are increased a little by the giving way of the soft parts.--G H, is the transverse, or bis-ischiatic diameter; it measures _four inches_. [Illustration: Plate X. The Bones of the Pelvis viewed from below, looking through the inferior strait, to show its diameters.] It will thus be seen that the diameters only average from four to five inches, but it must be remembered that the soft parts, and even one of the bones, very readily give way, and thus they are slightly increased.