THE COXAL BONE 169 



Occasionally sesamoids occur over the metacarpo-phalangeal joint of the third and fourth digits, 

 and an additional one may occur over that of the fifth. 



Very rarely a sesamoid is developed in the tendon of the biceps over the tuberosity of the 

 radius. 



B. THE BONES OF THE LOWER EXTREMITY 



The bones of the lower extremity may be arranged in four groups correspond- 

 ing to the division of the limb into the hip, thigh, leg, and foot. In the hip is the 

 coxal or hip-bone, which constitutes the pelvic girdle [cingulum extremitatis 

 inferioris], and contributes to the formation of the pelvis; in the thigh is the femur ; 

 in the leg, the tibia and fibula, and in the foot the tarsus, metatarsus, and phalanges. 

 Associated with, the lower end of the femur is a large sesamoid bone, the patella 

 or knee-cap. 



THE COXAL BONE 



The coxal (innominate) bone or hip-bone [os coxae] (figs. 205, 206) is a large, 

 irregularly shaped bone articulated behind with the sacrum, and in front with its 

 fellow of the opposite side, the two bones forming the anterior and side walls of 

 the pelvis. The coxal bone consists of three parts, named ilium, ischium, and 

 pubis, which, though separate in early life, are firmly united in the adult. The 

 three parts meet together and form the acetabulum (or cotyloid fossa), a large, 

 cup-like socket situated near the middle of the lateral surface of the bone for 

 articulation with the head of the femur. 



The ilium [os ilium] is the upper expanded portion of the bone, and by its 

 inferior extremity forms the upper two-fifths of the acetabulum. It presents for 

 examination three borders and two surfaces. 



Borders. — When viewed from above, the thick crest [crista ihaca] or superior 

 border is curved somewhat like the letter /, being concave medially in front and 

 concave laterally behind. Its anterior extremity forms the anterior superior 

 iliac spine, which gives attachment to the inguinal (Poupart's) ligament and the 

 sartorius; the posterior extremity forms the posterior superior iliac spine and 

 affords attachment to the sacro-tuberous (great sacro-sciatic) ligament, the pos- 

 terior sacro-iliac ligament, and the multifidus. The crest is narrow in the middle, 

 thick at its extremities, and may be divided into an inner lip, an outer lip, and an 

 intermediate line. About two and a half inches from the anterior superior spine 

 is a prominent tubercle on its external lip. 



The external lip of the crest gives attachment in front to the tensor fascice latce; along its 

 whole length, to the fascia lata; along its anterior half to the external oblique; and behind this, 

 for about an inch, to the latissitnus dorsi. The anterior two-thirds of the intermediate line 

 gives origin to the internal oblique. The internal lip gives origin, by its anterior two-thirds, to 

 the transversus; behind this is a small area for the quadratus lumborum, and the remainder 

 is occupied by the sacro-spinalis {erector spince). The internal lip, in the anterior two-thirds, 

 also serves for the attachment of the iliac fascia. 



The anterior border of the ilium extends from the anterior superior iliac spine 

 to the margin of the acetabulum. Below the spine is a prominent notch from 

 which fibres of the sartorius arise, and this is succeeded by the anterior inferior 

 iliac spine, smaller and less prominent than the superior, to which the straight 

 head of the rectus and the ilio-femoral ligament are attached. On the medial side 

 of the anterior inferior spine is a broad, shallow groove for the ilio-psoas as it 

 passes from the abdomen into the thigh, limited below by the ilio-pectineal 

 eminence, which indicates the point of union of the ilium and pubis. 



The posterior border of the ilium presents the posterior superior iliac spine, 

 and below this, a shallow notch terminating in the posterior inferior iliac spine 

 which corresponds to the posterior extremity of the auricular surface and gives 

 attachment to a portion of the sacro-tuberous (great sacro-sciatic) ligament. 

 Below the spine the posterior border of the ilium forms the upper limit of the 

 greater sciatic notch. 



Surfaces. — The external surface or dorsum is concave behind, convex in front, 

 limited above by the thick superior border or crest, and traversed by three gluteal 

 lines. 



