HIP-JOINT, NORMAL ANATOMY OF (in human anatomy).—Fr. articulation iliofemorak ; Germ. Iluft gclenk.—This joint belongs to the class of enarthrodial or ball and socket joints, being formed by the adaptation of the head of the femur to the acetabulum of the os innominatum. These bones are con nected by a very powerful capsular ligament, which again is completely covered by strong and thick muscles, under theinfluence of which the various motions of the joint are performed. We propose to examine seriatim the several textures entering into the formation of this joint, and lastly to consider the motions of which it is susceptible.
The bones.—Of the two bones which in the adult enter into the formation of this joint, the os innominatum contributes by the acetabulum, and the femur by its head.
acetabulum (cotyloid cavity: Germ. die Panne) is the cup or socket which receives the head of the femur, and is admitted to be the deepest articular cavity in the body. Prior to the adult period of life this cavity serves as the centre of union for the three bones of which the os innominatum is formed, viz., the ilium, ischium, and pubis. These, however, do not enter equally into the acetabulum, inas much as the ischium contributes in the pro portion of rather more than two-fifths, the ilium of about two-fifths, whilst the pubis yields la ther less than one-fifth.
Although the acetabulum is situated nearly in the centre of the separated os innominatum, it has a different position in relation to the entire pelvis. The union of the ossa innomi nata at the symphysis pubis, and the comple tion of the pelvis by the addition of the sacrum posteriorly, place the acetabular cavities on either side upon the antero-external aspect of the pelvis, so that a line drawn horizontally from the one to the other would pass through the union of the anterior with the two posterior thirds of the antero-posterior diameter of the pelvis. The aspect of each acetabulum is out wards and very slightly forwards as well as downwards.
Each cavity is surrounded for about four fifths of its circumference by a sharp but strong lip or margin (supercilium acetabuli), leaving opposite the obturator foramen a notch of considerable extent occtabuli) di rected from without downwards, forwards, and inwards, the deepest part of which is smooth and gives passage to nerves and vessels. This
notch corresponds to the junction of the pubis and ischium ; and we may here observe that the margin of the acetabultim exhibits a slight concavity superiorly, corresponding to the junction of the pubis and ilium, and a similar one inferiorly and externally, corresponding to the junction of the ilium and isehium. These concavities are separated by intervening con vexities, and hence the margin of the acetabu lum has the appearance of a waving line. Immediately within the margin of the acetabu him we perceive a broad band of smooth bone Varies Janata) covered in the recent state by articular cartilage, about seven-eighths of an inch wide at its lower portion, or oppo site the ischium, an inch and a quarter to an inch and a half superiorly and externally, where it corresponds to the ilium, and from a quarter to half an inch internally and superiorly at the pubis. This band terminates at each extremity of the notch already described in a process (corm ), the superior of which looks downwards, outwards, and backwards, whilst the inferior, more prominent than the superior, projects towards the notch, forming a kind of gutter between its superior margin, and the deepest part of the notch. Internal to this band, there is a depression, as it were a cavity within the acetabulum, rough and uneven, uninvested by cartilage in the recent state, being continuous with the notch leading towards the obturator foramen. This is the fovea or sinus, and lodges a quantity of fatty cellular tissue formerly termed glands Havers, from their having been first described by that anatomist. On the upper and lower portions of this inner cavity, various inequalities and foramina are seen, the latter being for the pas sage of the nutritious vessels of the bone, which is very thin at this point, so much so in deed, that if held up to the light, it will be found transparent. 'I he depth of the acetabu lum is not uniform in its different regions. This variety corresponds in a great measure to the breadth of the smooth band of bone (liteies lunata) already described. Where this is broadest, the cavity possesses the great est depth, and where it is entirely absent, the cavity is very superficial, as opposite the notch.