PELVIS. 



117 



lowed, rough, and broad in front, for the 

 attachment of some muscles of the leg. There 

 are numerous nutritious openings on this sur- 

 face of theischium and pubis, which are chiefly 

 directed towards the cotyloid cavity. 



Fig. 77. 



Internal view of the os innominatum, 



The infernal or pelvic surface presents for 

 examination a superior or iliac portion di- 

 rected forwards, upwards, and inwards, and 

 an inferior ischio-pubic portion directed in- 

 wards and backwards. 



The iliac portion is rough at the posterior 

 third, and is marked by a thick, massy, irre- 

 gular prominence, just below the posterior 

 extremity of the crest, which is continued to 

 the posterior superior spine, and serves for 

 the attachment of powerful ligaments which 

 connect this bone to the sacrum. This may 

 be called, for brevity, the iliac tuberosity (1). 



An inch and a half below this is an angu- 

 lar or semilunar articular surface, the sacral, 

 or .auricular (<J), to which the sacrum is at- 

 tached in the complete pelvis. This surface 

 is generally more or less rough and irre- 

 gular, for the more firm attachment of the 

 articular cartilage. It is composed of two 

 elongated portions placed at right angles to 

 each other, of which the inferior is the longer, 

 and is directed horizontally backwards to the 

 posterior interior spine, parallel with and close 

 above the upper boundary of the great sciatic 

 notch (m, n), while the superior is directed 

 vertically upwards towards the crest of the 

 ilium, to which its raised anterior border is 

 prolonged by a well marked ridge (3). At the 

 angle of junction of these two limbs is gene- 

 rally to be seen a deep hollow, while the ex- 

 tremity of the inferior limb is bevelled off to 

 correspond to elevations on the opposed sur- 

 faces of the sacrum. In the retiring an^le 

 formed bv the auricular surface is a very roujjh 



depression for the attachment of inter-osseous 

 ligaments (7). 



The anterior two thirds of the internal 

 iliac surface forms a complete smooth and 

 regular hollow called the internal iliac fossa 

 (4) for the reception of a muscle, which is 

 continued downwards and forwards into the 

 groove before described, below the anterior 

 inferior spine of the ilium (V/toe). At a small 

 distance in front of the articular surface, is 

 a large nutritious opening, directed down- 

 wards and forwards towards the cotyloid 

 cavity, for the passage of the principal nu- 

 tritive artery of this bone. Many others of 

 less calibre, all directed downwards, also exist 

 on this surface. Passing downwards and for- 

 wards from the angle of the sacro-iliac arti- 

 cular surface is a thick, rounded and arched 

 ridge of bone (5), which serves to transmit 

 the weight of the spine from the sacral arti- 

 cular surface to the femur at the cotyloid 

 articulation. Just behind the ilio-pectineai 

 eminence, before described, this line becomes 

 more salient, and passes from this point to 

 the spine of the pubes as a well marked pro- 

 jecting crest, the illo-pcctlncnl line (6), which 

 serves for the attachment of a muscle of the 

 leg, and some strong fasciae. The internal 

 surface of the pubis and ischium, and the 

 small inferior, or true pelvic portion of the 

 ilium, are seen below this line, which separates 

 them from the iliac fossa. Posteriorly is 

 seen a broad, flat surface (p), to which is op- 

 posed the cotyloid cavity externally, and the 

 rough lines, marking the junction of the three 

 component bones, are repeated more strongly 

 and more extensively here than in the coty- 

 loid cavity itself. They form a Y shape, the 

 posterior limb of which is directed backward 

 to the top of the great sciatic notch ; one 

 branch terminates at the pectineal eminence ; 

 and the other at the obturator opening, where 

 it passes into the commencement of the sub- 

 pubic groove (t,), the termination of which 

 was described with the external surface. An- 

 teriorly is seen the inner aspect of the obtu- 

 rator foramen (o). and the posterior surfaces, 

 and slightly marked line of union of the 

 branches of the pubis and ischium (r, s), 

 which are smooth, rounded off, and laterally 

 convex for the apposition of the pelvic viscera. 

 Below is the inner aspect of the great tuber- 

 osity of the ischium (2), which is also smooth 

 and concave for the like purposes. 



Infernal structure of the innominate bone. 

 Like other irregular bones, the haunch- 

 bone is composed of canccllous structure, 

 encased in layers of laminated bone, more 

 or less thick, as strength and tenacity are re- 

 quired. The thickest and strongest part of the 

 haunch-bone is the arched, rounded rib, ex- 

 tending from the cotyloid cavity to the au- 

 ricular surface and tuberosity of the ilium, 

 which is the direct line of pressure from the 

 spine to the legs, A cross section of this 

 part of the bone is nearly an inch in diameter, 

 generally, at its narrowest point. The de- 

 scending rami of the ischia are the next 

 in point of strength, for supporting the body 



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