PELVIS. 



197 



will have a tendency to become flattened 

 antero-posteriorly, by the sinking of the pubic 

 arch, at the same time that the traction of 

 the femurs and muscles of the lower extremi- 

 ties outwards will tend to separate the aceta- 

 bula and increase the transverse diameters. 

 This I apprehend to be the commencement of 

 the elliptical pelvic deformity, which occurs in 

 the majority of the softened pelves of infants, 

 whose most frequent and long-continued po- 

 sition is the dorsal recumbent. The angles 

 of the pelvis with the spine will also have 

 a tendency in this posture to become in- 

 creased by the weight of the inferior extremi- 

 ties. If the softening be great, and the 

 position long-continued, the symphysis pubis 

 would also sink, producing the hour-glass 

 form of pelvis ; a disposition which would be 

 increased by the traction of the levator ani 

 and weight of the bladder. There w r ould also 

 be a tendency to flattening of the sacrum. 

 In lying upon the side, on the other hand, 

 there is a pressure, through the trochanters, 

 upon the acetabula, which, if long and fre- 

 quently-accustomed, will cause the lateral 

 pelvic arches to yield and bend inwards at 

 the cotyloid line of junction, in children as 

 yet unossified, and produce the first bend or 

 tendency to the angular deformity. The 

 effect of these first impressions are, as Dr. 

 Ramsbotham observes, illustrated by making 

 an elbow in a piece of wire subjected to 

 pressure at each extremity. In the unde- 

 veloped pelvis also, the facility with which 

 these impressions are made upon the pubic 

 tie is rendered greater by the greater tardiness 

 of its ossification than" in the other innomi- 

 nate pieces. In some instances, pelves seem 

 to have been impressed in this manner on one 

 side only, so that the two sides present an 

 approach to the two different varieties of de- 

 formity, as will be presently alluded to. 



In the sitting and standing positions, a more 

 powerful distorting influence is brought into 

 play viz. the pressure of the weight of the 

 body on the softened pelvic arches. 



The sitting posture, when the elliptical form 

 has already been impressed upon the pelvis, will 

 still further tend to separate the .acetabula by 

 the starting outwards of the lower extremities 

 of the ischio-sacral arch under the pressure 

 of the weight of the trunk on the sacrum ; 

 and thus the separation of the tuberosities, 

 the enlargement of the transverse diameter of 

 the outlet, and the spreading out of the sub- 

 pubic arch take place. At the same time 

 the sacral promontory sinks into the pelvis 

 under the weight of the trunk, while the lower 

 part of the sacrum is kept forwards by the 

 sciatic ligaments, so that a bend takes place 

 in the middle of the bone. This bend will be 

 still further increased by the divergence of 

 the ischial tuberosities, permitting the weight 

 of the spine to be brought to bear upon the 

 coccyx and lower end of the sacrum and 

 against the sitting surface. The total direc- 

 tion of the pressure on the ischial tuberosities 

 being upwards and backwards, the curve of 

 the ischio-sacral arch (coinciding with that of 



the cotylo-sacral at the top of the sciatic 

 notch) takes place in that direction, and in- 

 creases the acuteness of the C-like curve. 



These effects upon the sacrum and ilia, 

 and pelvis generally, will be increased by 

 the action of the powerful erector spinas 

 muscles, and psoas and iliacus muscles, exer- 

 cised in keeping the trunk erect upon the 

 pelvic lever (see fg. 122 E, c d). These 

 muscles have, in addition, much influence in 

 shortening the spinal column itself, already 

 bending under the weight of the body, and, 

 following the general tendency of elongated 

 substances yielding to pressure at both ends 

 to twist laterally, the lumbar curve and sacral 

 promontory become placed on one side the 

 median line. This tendency, from reasons 

 before explained, is generally to the left. 

 Under the increased inclination of the pelvic 

 angle, the abdominal muscles will tend to 

 draw the flattened pubes upwards still nearer 

 the sacral promontory, diminishing the con- 

 jugate diameter. In 'extreme deformity, the 

 iliac wings are pressed still further outwards 

 and everted by the pressure of the lower ribs 

 resting upon them, as we have observed in one 

 of the detailed examples. 



But when the lateral pelvic arches are al- 

 ready impressed with the angular deformity, 

 the sitting posture has the effect of merely 

 increasing the inward bend, and approximat- 

 ing the acetabula and sc'atic tuberosities to 

 the sacrum, pressed down by the superin- 

 cumbent weight. Dr. Rigby mentions that 

 frequent riding on horseback at an early age 

 will produce contraction of the inferior outlet, 

 even in the healthy pelvis, and that the females 

 of those American nations who ride much bear 

 few children, and are often three or four days 

 in severe labour. 



In certain cases, in which the acetabulum 

 on one skle only has been pressed inwards by 

 the constant use of the lateral recumbent po- 

 sition, or in which the centre of gravity of the 

 trunk has been permanently shifted to one 

 side by the spinal bend, a habit is acquired of 

 sitting more upon one ischial tuberosity thar 

 the other. This unequal pressure produces 

 inequality of distortion, and presses the tu- 

 berosity and acetabulum of that side inwards, 

 while the opposite one presents the usual di- 

 vergence of the elliptical distortion. This 

 effect is also contributed to in like manner, 

 under the same circumstances, in the standing 

 position, by the pressure being greater and 

 more frequent upon one fenfur than the 

 other ; and thus we have produced a sort of 

 oblique deformity, of which 1 have seen se 

 veral specimens/ 



In the Museum of King's College are three 

 skeletons, all presenting more or less a ten- 

 dency to this peculiar modification of the 

 ovate deformity. In the Hunterian Museum 

 is another, in an adult female skeleton, still 

 more marked. 



It is somewhat remarkable that, in all these 

 examples, the trunk is bent towards the right 

 side, and the lumbar curve and sacral projection 

 towards the left; so that the line of gravity, and 



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