The Lower Extremity and Pelvis 127 



true transverse fibres on the back of the joint, and only a few of the inner marginal 

 fibres of the circular group run to the bone in this region : a group of these below 

 reach the upper ramus of ischium as the " ischio-capsular band." 



The posterior surface of the acetabular mass is covered by Pyriformis, and may 

 give origin to some fibres of Glutens minimus deep to this : the sciatic nerves, etc., 

 and nerve to Quadratus femoris pass down on it. The thin floor of the acetabulum 

 is occasionally, like the thinnest part of the iliac fossa, found to be perforated, and 

 the hole is then closed by membrane. 



Dorsum Ilii. -The curved lines separate the gluteal planes. The upper or posterior 

 line commences just in front of the posterior inferior spine and reaches the crest about 

 2\ inches in front of the upper spine. Gluteus maximus arises behind it, and can 

 therefore extend directly on to the great sciatic ligament, which is fastened to the 

 lower spine and the margin of the notch just in front of this (see Fig. 107), and can thus 

 reach the sacrum. The middle line commences near the deepest part of the greater 

 notch and ends about 2 inches behind the anterior superior spine : observe (Fig. 107) 

 that the line does not actually reach the outer lip of the crest. Gluteus medius arises 

 between this line and the upper one, and some of its deeper posterior fibres may be 

 separated from it as an additional origin of Pyriformis from the top of the notch : 

 just in front of this the margin of the notch may be slightly grooved by the Gluteal 

 art ery. 



FIG. 106. To illustrate the formation of the ligamentum teres. In its early stage the ilium (il) and ischium 

 (is) are alone concerned in the articulation, the synovial lining passing off them on to the capsule which 

 is attached round their surfaces. The pubis is covered by these fibres and has no articular area. In 

 the next stage the covering fibres are destroyed and the pubis has acquired an articular surface (/>). 

 This extends, and the front part of the original ischial capsule is caught, so to speak, between the 

 extending surface and the ischium ; these fibres persist and remain attached to the ischial region, but 

 on their surface the synovial cavity has extended, as shown in the last diagram, and has joined the 

 older cavity below as well, passing between the femur and the lower portion of the attached capsule. 

 Thus a synovial funnel is formed, wider below where it includes the attachment of the fibres and 

 narrowed at its femoral end, where it is fastened to the fovea. 



FIG. 107. Postero-external aspect of right os innominatum. The curved lines are somewhat diagram- 

 matically drawn : for account see the text. Some of the fibres of the great sciatic ligament run on to 

 the surface of the bone round x, and give origin here to part of G. maximus. The position of the sacrum 

 and great ligament is indicated, with the origin of the muscle from it. A is the surface below the 

 inferior curved line, covered by G. min. ; B, the area covered by Pyriformis, with the great sciatic 

 nerve interposed ; C, covered by Obturator internus and Gemelli, which lie between the nerve and the 

 bone, but have the nerve to Quadratus between them and the bone. The muscles mentioned are 

 practically in a continuous curved plane, so that the areas A, B, and C make a convex surface, con- 

 tinuously curved and smooth, round the acetabulum ; the muscles pass to the raised trochanter, so do 

 not mould the bone by pressure. The lower aspect of the tuber ischii, below the facets for the ham- 

 string muscles, shows two sloping surfaces, of which one looks outwards and gives origin to fibres of 

 Adductor magnus (ischio-condylar portion), while the other looks inwards (D) and is covered by fibro- 

 fatty tissue which is continuous round the great sacro-sciatic ligament with that of the ischio-rectal 

 fossa : in this tissue is a badly-defined bursa which lies under the tuberosity in sitting, the hamstrings 

 and Adductor moving to the outer side of the prominence when the limbs are bent for that purpose. 



The lower curved line is variable as to its commencement : it is directed toward 

 the upper part of the anterior inferior spine, or toward the notch above this. 



But the arrangement of the lines is not quite so simple as this description implies and by 

 comparing several bones the following account can be verified. 



The Gluteus maximus is in the same curved plane as the Tensor fasciaa femoris, which arises 

 from the bone just below the crest for about 3 inches behind the anterior superior spine. The two 

 muscles are connected by a strong aponeurotic sheet, the Gluteal aponeurosis, which splits behind 

 to enclose G. maximus, and in front to enclose the Tensor : between these two it covers the medius 

 and is attached to the outer edge of the crest. On the bone the line of this aponeurosis is easily 

 followed, and the layer that passes deep to maximus is seen to form the superior curved line and so 

 reach the great sciatic ligament. Again, in front, the line on the bone is seen to divide to enclose 



