Bones of the Lower Extremity. 115 



The OS coxae (hip bone) (0. T. os innominatum) (see also Figs. 153 167) is paired, 

 lies in the lowermost part of the trunk, and forms there with the same bone of the other side 

 and with the sacrum a firm broad bony ring upon which the vertebral column rests above 

 and with which, externally, the bones of the thigh are connected. 



Each os coxae is composed of three pieces, separated until about the age of puberty: 

 the os ilium which is directed upward and backward, the os ischii, which is directed downward 

 and backward and the os pubis which is directed forward and downward. These three 

 constituents meet somewhat below the middle of the hip bone. At this spot on the external 

 surface lies a wide deep fossa, the acetabulum. This is surrounded by a high bony wall which 

 presents below a broad notch, the incisura acetabuli; in the bottom of the acetabulum a large 

 rough spot is visible, the fossa acetabuli, which is surrounded in front, above and behind by 

 a horse-shoe-shaped concave surface, the fades lunata, covered with cartilage. The acetabulum 

 serves for articulation with the femur. In youth the places where the three bones unite are 

 visible as a Y-shaped seam, the middle point of which is situated in the fossa acetabuli. 



The os ilium (see also Figs. 153 155 and 157 167) helps to form the acetabulum 

 by means of its thick and broad lower part , the corpus ossis ilium (vide supra) ; the upper 

 part is a broad, in places very thin, somewhat wavy bony plate which bends backward, up- 

 ward and lateralward and is called the ala ossis ilium. The corpus and ala are separated 



from one another by the linea arcuata, a curved rounded bony ridge descending obliquely from 



tr 1 

 behind and above, forward and downward. A The free margin of the ala ossis ilium is curved like 



the letter S, being concave medianward in front and convex median ward behind; elsewhere it 

 is markedly broadened; it is called the crista iliaca (iliac crest). On it the places of 

 attachment of the abdominal muscles are marked as ridges, namely as labium externum and 

 labium inter num on the external and internal angle of the crest and as linea intermedia 

 between these two. The crest ends in front in a blunt projection, spina iliaca anterior 

 superior; below this the margin is narrower, somewhat concave and presents a second less 

 marked projection, spina iliaca anterior inferior-, below this it goes over into the corpus 

 ossis pubis and there forms with the latter the eminentia iliopectinea. The iliac crest ends 

 behind at the spina iliaca posterior superior ; below it, separated by a small notch, lies the 

 spina iliaca posterior inferior (sometimes indistinct), and still lower is a deep notch involving 

 also the corpus ossis ischii, the incisura ischiadica major (0. T. great sacro-sciatic notch). 

 The medial surface of the ala is for the most part, smooth, slightly concave, the fossa iliaca; 

 behind it is an uneven portion, the anterior half of which, fades auricular is, covered with 

 cartilage, articulates with the facies auricularis ossis sacri, while its posterior, . very rough half, 

 tuber ositas iliaca, serves chiefly for the attachment of the ligamenta sacroiliaca interossea. 

 The facies auricularis is not infrequently partially surrounded in front and behind by a groove, 

 the sulcus paraglenoidalis, which serves for the attachment of the deep fibrous bands of the 

 ligamenta sacroiliaca. The external surface of the ala is fairly cmooth, and curved so as to 

 be convex in front, concave behind. It presents three rough ridges, convex upward and back- 

 ward, the shortest of which, the linea glutaea inferior (0. T. inferior curved line), lies just 

 above the acetabulum; above and behind this is the linea glutaea anterior (0. T. middle 

 curved line) which is the longest of the ridges and extends from the incisura ischiadica major 

 to the spina iliaca anterior superior; and above this the shorter linea glutaea posterior 

 (0. T. superior curved line) runs from the spina iliaca posterior inferior to the crista iliaca. 



