Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/879

Rh -LOWER LIMB.] ANATOMY 829 like bone, the fundamental form of which is obscured by the modification in shape of its inner end. In human anatomy it is customary to regard it as consisting of a body and of two branches, a horizontal and a descending ramus. The body and horizontal ramus form the funda mental prismatic rod, and the descending ramus is merely a special offshoot from the inner end of the rod. The outer end of the rod takes a part in the formation of the acetabulum ; the inner end is expanded into the body of the pubis, and has a broad margin, or symphysis, for articulation with the corresponding bone on the opposite side of the pelvis. The three surfaces are a superior, for the origin of the pectineus muscle; a posterior, which enters into the wall of the true pelvis ; and an inferior, which forms the upper boundary of the obturator foramen. The descending ramus is merely a downward prolongation of the inner end of the bone which joins the ischium, and aids in forming the side of the pubic arch. The junction of the outer end of the pubis with the ilium is marked by the pectineal eminence. The superior and posterior sur faces are separated by the sharp pectineal line, which, starting from the spine of the pubis, runs outwards to aid in forming the brim of the true pelvis. The Ischium (Fig. 11), like the ilium and pubis, has the fundamental form of a three-sided prismatic rod. One extremity (the upper) completes the acetabulum, whilst the lower forms the large prominence, or tuber ischii. The surfaces of the bone are internal or pelvic, external, and anterior. The pelvic and external surfaces are separated from each other by a sharp border, on which is seen the ischial spine. The pelvic and anterior surfaces are sepa rated by a border, which forms a part of the boundary of the obturator foramen; but the margin between the external and anterior surfaces is feebly marked. The tuberosity, a thick, rough, and strong process, gives origin to several powerful muscles : on it the body rests in the sitting posture ; an offshoot, or ramus, ascends from it to join the descending ramus of the pubis, and com pletes both the pubic arch and the margin of the obturator foramen. By the articulation of the two innominate bones with each other in front at the pubic symphysis, and with the sides of the sacrum behind, the osseous walls of the cavity of the PELVIS are formed. This cavity is subdivided into a false and a true pelvis. The false pelvis lies between the expanded wing-like portions of the two ilia. The true pelvis lies below the two pectineal lines and the base of the sacrum, which surround the upper orifice or brim of the true pelvis, or pelvic inlet; whilst its lower orifice or outlet is bounded behind by the coccyx, laterally by the ischial tuberosities, and in front by the pubic arch. In the erect attitude the pelvis is so inclined that the plane of the brim forms with the horizontal plane an angle of jfrom CO to 05. The axis of the cavity is curved, and is (represented by a line drawn perpendicularly to the planes i of the brim, the cavity, and the outlet; at the brim it is
 * directed upwards and forwards, at the outlet downwards

and a little forwards. Owing to the inclination of the pelvis, the base of the sacrum is nearly 4 inches higher than the upper border of the pubic symphysis. The female pelvis is distinguished from the male by certain sexual characters. The bones are more slender, the ridges and processes for muscular attachment more feeble, the breadth and capacity greater, the depth less, the ilia more expanded, giving the greater breadth to the hips of a woman than a man; the inlet more nearly circular, the pubic arch wider, the distance between the tuberosities greater, and the obturator foramen more triangular in the female than in the male. The greater capacity of the woman s than the man s pelvis is to afford greater room for the expansion of the uterus during pregnancy, and for the expulsion of the child at the time of birth. The Femur or Thigh-bone (Fig. 11) is the longest bone Femur. in the body, and consists of a shaft and two extremities. The upper extremity or head possesses a smooth convex surface, in which an oval roughened fossa, for the attachment of the inter-articular ligament of the hip, is found; from the head a strong elongated neck passes downwards and out wards to join the upper end of the shaft; the place of junction is marked by two processes or trochanters: the external is of large size, and to it are attached many muscles; the internal is much smaller, and gives attach ment to the psoas and iliacus. A line drawn through the axis of the head and neck forms with a vertical line drawn through the shaft an angle of 30; in a woman this angle is less obtuse than in a man, and the obliquity of the shaft of the femur is greater in the former than in the latter. The shaft is almost cylindrical about its centre, but expanded above and below; its front and sides give origin to the extensor muscles of the leg; behind there is a rough ridge, which, though called linea aspera, is really a narrow surface and not a line; it gives attachment to several muscles. The lower end of the bone presents a large smooth articular surface for the knee-joint, the anterior portion of which forms a trochlea or pulley for the movements of the patella, whilst the lower and posterior part is subdivided into two convex condyles by a deep fossa which gives attachment to the crucial ligaments of the knee. The inner and outer surfaces of this end of the bone are rough, for the attachment of muscles and the lateral ligaments of the knee. The Patella or Knee-pan (Fig. 11) is a small triangular Patella. flattened bone developed in the tendon of the great extensor muscles of the leg. Its anterior surface and sides are rough, for the attachment of the fibres of that tendon; its posterior surface is smooth, and enters into the formation of the knee-joint. Between the two bones of the leg there are no move ments of pronation and supination as between the two bones of the fore-arm. The tibia and fibula are fixed in position; the fibula is always external, the tibia internal The Tibia or Shin-bone (Fig. 11) is the larger and Tibia, more important of the two bones of the leg; the femur moves and rests upon its upper end, and down it the weight of the body in the erect position is transmitted to the foot. Except the femur, it is the longest bone of the skeleton, and consists of a shaft and two extremities. The upper extremity is broad, and is expanded into two tuber osities, the external of which has a small articular facet inferiorly, for the head of the fibula; superiorly, the tuber osities have two smooth surfaces, for articulation with the condyles of the femur; they are separated by an intermediate rough surface, from which a short spine projects, which gives attachments to the inter-articular crucial ligaments and semilunar cartilages of the knee, and lies opposite the inter- condyloid fossa of the femur. The shaft of the bone is three-sided; its inner surface is subcutaneous, and forms the shin ; its outer and posterior surfaces are for the origin of muscles; the anterior border forms the sharp ridge of the shin, and terminates superiorly in a tubercle for the inser-. tion of the extensor tendon of the leg ; the outer border , of the bone gives attachment to the inter-osseous membrane of the leg. The lower end of the bone, smaller than the : upper, is prolonged into a broad process, internal malleolus, which forms the inner prominence of the ankle: its under^ surface is smooth for articulation with the astragalus ; exter nally it articulates with the lower end of the fibula. I The Fibula, or Splint-bone of the leg (Fig. 11), is a Fibula, slender long bone with a shaft and two extremities. The upper end or head articulates with the outer tuberosity of