Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/878

Rh f828 ANATOMY [SKELETON from the radial or outer to the ulnar or inner side of the wrist. It is unnecessary to give a separate description of &quot;each bone. Except the pisiform or pea-shaped bone, which articulates with the front of the cuneiform, each carpal bone is short and irregularly cuboidal in shape ; its anterior (or palmar) surf ace and its posterior (or dorsal) being rough, for the attachment of ligaments ; its superior and inferior surfaces being invariably smooth, for articulation with adjacent bones ; whilst the inner and outer surfaces are also smooth, for articulation, except the outer surfaces of the scaphoid and trapezium (the two external bones of the carpus), and the inner surfaces of the cuneiform and unciform (the two internal bones). Occasionally a ninth or supernumerary bone may arise from the subdivision of the scaphoid, semilunar, or trapezoid, into two pieces ; more rarely a distinct bone is found in the human wrist inter calated between the trapezoid, os magnum, semilunar, and scaphoid, which corresponds in position to the os inter medium, found constantly in the wrist of the orang, gibbon, the tailed apes, and many rodents and insectivora. Ji The Metacarpal bones, or bones of the Palm of the Hand, are five in number (Fig. 9). They are miniature long bones, and each possesses a shaft and two extremities. The metacarpal of the thumb is the shortest, and diverges outwards from the rest : its carpal extremity is saddle- shaped, for articulation with the trapezium ; its shaft is somewhat compressed, and its phalangeal end is smooth and rounded, for the first phalanx of the thumb. The four other metacarpal bones belong to the four fingers : they are almost parallel to each other, and diminish in size from the second to the fifth. Their carpal ends articulate with the trapezoid, os magnum, and unciform : their shafts are three-sided : their phalangeal ends articulate with the first phalanges of the fingers. i The number of Digits in the hand is five, which is the highest number found in the mammalia. They are dis tinguished by the names of pollex or thumb, and index, middle, ring, and little fingers. Their skeleton consists of fourteen bones, named phalanges, of which the thumb possesses two, and each of the four fingers three. The phalanx next the metacarpal bone is the first, that which carries the nail is the terminal or ungual phalanx, whilst the intermediate bone is the second phalanx. Each is a miniature long bone, with two articular extremities and an intermediate shaft, except the terminal phalanges, which have an articular surface only at their proximal ends, the distal end being rounded and rough, to afford a surface for the lodgment of the nail. The INFERIOR or PELVIC EXTREMITY, or LOWER LIMB, consists of a proximal part or haunch, a distal part or foot, and an intermediate shaft subdivided into thigh and leg. Each part has v its appropriate skeleton : in the haunch, the pel vic or innomi- nate bone ; in the thigh, the femur; in the leg, the tibia and fibula Fro. 10. Diagrammatic section to represent the relations /fV. tl 1 V&amp;gt; of the Pelvic Girdle to the Trunk. V, a sacral vertebra; ^tne inign- Done n_ the- ilium; P, the two pubic bones meeting in front in man being at the symphysis ; F, the femur. ^longer than the leg-bones) ; in front of the knee, the . patella ; in the foot, the tarsal and metatarsal bones and phalanges. The bone of the haunch forms an arch or Pelvic Girdle, which articulates behind with the side of the sacrum, and arches forward to articulate with the opposite haunch-bone at the pubic symphysis. It is the direct medium of connection between the axial skeleton and the shaft and foot, which form a free divergent Appendage. Eium. M .., The Os Tnnominatum, or Haunch-bone, is a large lire- Pelvic gular plate-like bone, which forms the lateral and anterior girdle, boundary of the cavity of the pelvis. In early life it con sists of three bones ilium, ischium, and pubis which unite about the twenty-fifth year into a single bone. These bones converge, and join to form a deep fossa or cup, the acetcibulum or cotyloid cavity, on the outer surface of the bone, which lodges the head of the thigh-bone at the hip-joint. One-fifth of this cup is formed by the pubes, and about two-fifths each by the ischium and ilium. At the bottom of the acetabulum is a depression, to the sides of which the interarticular ligament of the hip-joint is attached. From the acetabulum the ilium extends upwards and backwards, the ischium downwards and backwards, the pubis forwards and inwards. In front of the acetabulum is a large hole, the obturator or thyroid foramen, which is bounded by the ischium and pubes; behind the acetabulum is the deep sciatic notch, which is bounded by the ischium and ilium. The Ilium (Fig. 10) in man is a broad plate -like bone. In its most simple form, as in the kangaroo, it is a three- sided, prismatic, rod-like bone, one end of which enters into the formation of the acetabu lum, whilst the other is free, and forms the iliac crest. In man, notwithstanding its ex panded form, three surfaces may also be recognised, cor responding to the surfaces in the ilium of the kangaroo; and, as in that animal, the lower end aids in forming the acetabulum, while the upper end forms the iliac crest, which, in man, in conformity with the general expansion of the bone, is elon gated into the sinuous crest of the ilium. This crest is of great importance, for it affords attachment to the broad muscles which form the wall of the ab dominal cavity. One surface of the ilium is external, and marked by curved lines which subdivide it into areas for the origin of the muscles of the buttock ; another surface is anterior, and hollowed out to give origin to. the iliacus muscle ; the third, or internal, surface articulates FIQ. 11. The Appendicuiar skeleton posteriorly with the sacrum, whilst anteriorly it forms a part of the wall of the true pelvis. The external is separated from the anterior surface by a border which joins the anterior end of the crest, where it forms a pro cess, the anterior superior spine. About the middle of this border is the anterior inferior spine. Between the external and inter nal surfaces is a border on which are found the posterior superior and inferior spines ; between the anterior and internal surfaces is the pectineal border, which forms part of the line of separation between the true and false pelvis. The Pubis (Fig. 1 1 ) is also a three-sided, prismatic, rod- of the Left Lower Limb. II, ilium, Is, ischium, Pb, pubis, the three parts of the innominate bone ; F, femur; P, patella; Tb, tibia; Fb, fibula; Tr, opposite the seven tarsal bones; C, os calcis, forming promi nence of heel ; lit, opposite the five metatarsal bones; II, hallux or preat toe; II. second, III. third, IV. fourth, V. fifth or little toe. The dotted line HH represents the horizontal plane, whilst the dotted line V is in line with the vertical axis of the spine.