THE LOWER EXTREMITY. 



The Pelvic Girdle. — This consists of the two innominate bones, which join 

 each other in front, and the sacrum behind. While the thoracic girdle is adapted 

 to freedom of motion, the pelvic is fitted for strength and support. 



The study of the innominate bone should be preceded by a general idea of the 

 pelvis. A plane between the promontory of the sacrum and the top of the pubes 

 divides the pelvis into the false pelvis above, formed chiefly by the ilia, and the true 

 pelvis below. The latter presents the sacrum and coccyx behind, the arch of the 

 pubes in front and below, and the tuberosity of the ischium at the side. Behind this 

 is the sacro-sciatic notch, much reduced by ligaments. On the sides are the hip- 

 joints, and towards the front the obturator or thyroid foramen. 



THE INNOMINATE BONE. 



This ^ consists originally of the ilium, pubis, and ischium, each of which forms a 

 part of the hip-joint, but which fuse so completely that the lines of union are not 

 usually to be seen in the adult. The ilium forms the upper and posterior part of the 

 bone, the pubis the front, and the ischium the inferior. The two latter enclose the 

 obturator foramen. 



The Ilium. — The ilium," a plate of bone forming the side of the false pelvis 

 and a part of the true, may be said to have four borders. The superior border, 

 or crest,' very much the longest, is convex upward and outward. It connects two 

 tubercles, the anterior and posterior superior spines of the ilium, of which the former 

 is a knob overhanging the concave anterior border and giving attachment to Pou- 

 part's ligament and the sartorius, while the latter is less prominent. The crest has 

 a double lateral curve, the front half being convex externally and the posterior inter- 

 nally. It is thicker at the ends than in the middle, and presents also a thickening 

 near the middle of each curve, projecting on the convex side. There is an external 

 lip, from the whole length of which springs the fascia lata of the thigh, an internal 

 lip, and an intermediate space. The anterior border is short, rounded, and con- 

 cave descending to the anterior inferior spine, a knob a little above the border of 

 the acetabulum giving origin to the straight head of the rectus femoris and a part of 

 the ilio-femoral band of the capsule of the hip-joint. The posterior border, very 

 short and also concave, ends in the posterior inferior spine, an ill-marked angle at 

 the bottom of the surface that joins the sacrum. The inferior border consists 

 anteriorly of an attached part, which meets the other bones in the acetabulum, and 

 behind this of a free concave part, which bounds the upper part of the great sacro- 

 sciatic notch.* The ilium might also be described as consisting of an expanded por- 

 tion, narrowing below to a stem, which joins the other bones in the acetabulum. Its 

 upper part follows the curves of the crest. 



The lateral or outer surface is crossed by the three curved or gluteal lines, 

 convex above and behind, all ending at or near the sciatic notch. The superior, 

 much the strongest, arises from the crest at the middle of its second curve and ends 

 a little in front of the posterior inferior spine, marking of? a raised rough surface 

 behind its upper two-thirds. The middle begins at the crest, one or two inches 

 from the anterior superior spine, and ends near the top of the notch. The inferior, 

 the faintest, starts a little above the anterior inferior spine and is lost near the 

 front of the notch. The three gluteal muscles, maximus, medius, and minimus, 

 arise respectively behind these three lines in the order given. A slight groove 

 for the reflected tendon of the rectus femoris, starting at the anterior inferior spine, 

 runs backward above the acetabulum. 



The ventral or inner surface is divided into an upper posterior and 

 a lower anterior part by the ilio-pcctiyieal line^ in front, and a rough border con- 

 tinuing it. The former is a line beginning on the pubis and continued across the 



' Os coxae. "Os ilium. •^ Crista iliaca. '' li cisiTa ischiadica major ^ Linea arcnata. 



