The ilia and ischia on each side are pushed together upwards and towards the sacrum, so that the acetabula are thereby approximated and placed nearer to the sacral prornontory. The cotylo-sacral arch presents, in most instances, a very sharp curve near the sacro-iliac joint, and is often bent double, so as to offer a mere chink between the sacral and iliac portions. The iliac wings are generally approximated, the venter being sometimes doubled into a mere fissure, and the crest being curved inwards more than normal, so as to bring the anterior superior iliac spines nearer together ; while the posterior extremity of the crest, or iliac tuberosity, is bent inwards and forwards over the sacrum, by the weight of the body, acting through the sacro-iliac ligaments. Thep/one:, spines, and tuberosities of the ischia are pushed inwards towards each other, and sometimes turned more upwards, so as to cause a chink or acute bend in the ischial plane, passing downwards and forwards, and which has been compared by Naegele to the fold made by bending pasteboard. The superior rami of the pubes are directed horizontally forwards, being almost, and, in extreme cases, quite pa rallel to each other anteriorly.
This alteration in the direction of the pubic bones takes place, in many cases, by an inward curve in the acetabula at the point of junction of the three pieces of the innominate bone, as indicated by the ilio pectineal eminence, and the form of the brim will then assume the shape of the letter Y when the deformity is great. In many in stances, however, the superior pubic rami are bent inwards at an obtuse angle, in the centre, just above the obturator foramina, the bones of the opposite sides almost or entirely meeting at the angle, and continuing parallel with each other to their articulation. The form of pelvis resulting from this bend in the superior pubic ramus has received more par ticularly the name of the cocked hat or ros trated pelvis; the latter name being applied front the beak-like projection of the pubis at the symphysis. It is markedly distinguished from those angular deformities in which the inward bend of the innominate bones takes place at the acetabular junction of their three component pieces, and is found exemplified in most of the specimens exhibiting the greatest contraction of the diameters.
The pubic symphysis is, in every case, more or less folded back, straining upon the anterior ligaments. The bending, however, is seen to occur in the osseous portions of the articula tion forming the pubic angles, generally about the position of the pubic spine, and it is much more considerable in the cases where the an terior portions of the pubes are parallel to each other. The sub-pubic arch is, in all
cases, very considerably narrowed by the parallel position of the superior pubic rami and the approximation of the ischial tu berosities. ln many instances, the latter appear to be pushed forwards and upwards, so that the contraction of the sub-pubic arch is greatest at the ischial rami, just above the tuberosities, above which point the sides of the arch bulge outwards. In the rostrated pelvis, it is often completely obliterated or transformed into a mere chink. The acetabula are elevated and turned more forwards than normal, and in many examples of rostrated pelvis are directed almost quite anteriorly.
The ang,les of both the superior and inferior pelvic planes with the vertebral column are lessened. In a case given by Naegele, the supe rior plane was at right angles to the spine. The a.ris of the brim is thus rendered more vertical, and that of the outkt more forward, than in the standard pelvis. The superior plane is often bent into two by the elevation of the acetabula, but, in some instances, the pubic symphysis is pushed upwards above the acetabula.
The d;ameters are all contracted in a greater or less degree, those of the brim most ex tensively. In this kind of pelvis occurs the greatest diminution of diameters of all the re corded examples. The diminution, however, is such, that if the irregular form were re shaped, the diameters would be replaced, e. there is no absolute shortening of the bones, or not so much as in the rickety pelves.
Examples.—The pelvis of Isabel Redman (fig. 11S.), upon whom hysterotomy was per formed by Dr. Hull in 1794, and which is said to present at the brim the most contracted diameters on record, is affected by this de formity in its rostrated form to such an extent, that a ball 111 inch in diameter would not pass through it at any part.
At the brim, the 4th lumbar vertebra was completely sunk into the pelvis, and in clined to the left side, and its distance from the pubic symphysis was 2-4- inches. The distance between the superior pubic mai at the point of angular bend, was * of an inch. From the 4th lumbar vertebra at its upper anterior border, to the left acetabulum, was only * of an inch ; on the right side *. The greatest transverse diameter was 53 inches. At the outlet, the distance between the sciatic tuberosities was 3* inches ; between the spines 2*. The greatest contraction of sub pubic arch was at the sciatic rami, which were only -17, of an inch distant from each other ; above this, the arch bellied out. The sacrum was bent double, so that the tip of the coccyx was only 1,1,s inch from the sacral base. The pelvic bones were quite soft, and lighter than natural.