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both of its margins, but more extensively to the postero-inferior. This ligament does not entirely fill the notch, but leaves an open interval between its inferior border and the bottom of the notch through which vessels and nerves enter the cup. The acetabular aspect of this ligament constitutes an articular surface.

The acetabulum is deepened by the labrum glenoidale (O.T. cotyloid ligament) (Figs. 315 and 316), which consists of a strong ring of fibro-cartilaginous tissue attached to the entire rim of the cup. The attached surface of the ring is broader than its free edge, and, moreover, the latter is somewhat contracted, so that the ligament grasps the head of the femur which it encircles. Its fibres are partly oblique and partly circular in their direction. By the former it is firmly implanted on the rim of the acetabulum and the lig. transversum acetabuli; by the latter the depth of the cup is increased through the elevation of its edge, and its mouth slightly narrowed. By one surface this ligament is also articular:

Capsula Articularis.—An articular capsule (Figs. 315 and 316) completely invests the joint cavity. Its fibrous stratum is of great strength, although it is not of equal thickness throughout, being considerably thicker on the supero-anterior aspect than at any other part. Unlike the corresponding structure of the shoulderjoint, it does not permit of the withdrawal of the head of the femur from contact with the acetabular articular surfaces, except to a very limited extent. Its fibres are arranged both in the circular and in the longitudinal direction, the former, known as the zona orbicularis, being best marked posteriorly, while the longitudinal fibres stand out more distinctly in front, where they constitute special ligaments. Looked at as a whole, the fibrous stratum of the capsule has the following attachments : proximally it surrounds the acetabulum, on the superior and posterior aspects of which it is attached directly to the hip bone, while on the anterior and inferior aspects it is attached to the non-articular surfaces of the labrum glenoidale and transverse ligaments of the acetabulum; distally it encircles the neck of the femur, where it is attached in front to the intertrochanteric line; above, to the medial aspect of the root of the greater trochanter; below, to the lower part of the neck of the femur, in close proximity to the lesser trochanter; behind, to the line of junction of the lateral and middle thirds of the neck of the femur. It is a matter of some importance to note that only part of the posterior surface of the neck of the femur is enclosed within the articular capsule. The femoral attachments of the fibrous stratum of the capsule vary considerably in their strength, being particularly firm above and in front, but much weaker below and posteriorly, where the orbicular fibres are well seen. Many fibres of the fibrous stratum, are reflected from its deep aspect proximally upon the neck of the femur, where they form ridges, and to these the term retinacula (Fig. 315) is applied.

The epiphyseal line of the head of the femur is intra-capsular; the epiphyseal lines of the two trochanters are extra-capsular.

The longitudinal fibres of the fibrous stratum of the capsule are arranged so as to form certain definite bands, viz. ::

(1) Lig. Iliofemorale.- The ilio-femoral ligament (Fig. 316) consists of a triangular set of fibres attached proximally, by their apex, to the inferior part of the anterior inferior iliac spine and the immediately adjoining part of the rim of the acetabulum, and distally, by their base, to the intertrochanteric line of the femur. This ligament is the thickest part of the fibrous stratum, but its sides are more pronounced than its centre, especially towards its base. Consequently the ilio-femoral ligament presents some resemblance to an inverted y(«), and therefore was formerly named the Y-shaped ligament of Bigelow.

The lateral or upper limb of the ilio-femoral ligament may be somewhat extended by the inclusion of additional longitudinal fibres, and described as the ilio-trochanteric ligament. This band arises from the anterior part of the dorsum of the acetabulum, and extends to the femoral neck, close to the anterior end of the medial surface of the greater trochanter.

(2) Lig. Pubocapsulare. - The pubo-capsular ligament (Fig. 316) is composed of some bands of fibres of no great strength, which extend from the lateral end of the superior ramus of the pubis, the ilio-pectineal eminence, the obturator crest and the obturator membrane, to lose themselves, for the most part, in the capsule, although

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a certain proportion of them may be traced to the inferior aspect of the femoral neck, where they adjoin the distal attachment of the ilio-femoral ligament.

(3) Lig. Ischiocapsulare.—The ischio-capsular ligament consists of a broad band of short, fairly strong longitudinal fibres, which, by their proximal ends, are attached to the ischium between the lesser sciatic notch and the obturator foramen, while their distal ends become merged in the zona orbicularis of the general capsule.

Within the capsule, and quite distinct from it, there are the ligamentum teres and the Haversian gland.

Lig. Teres Femoris.—The round ligament (Fig. 315) is a strong, somewhat Hattened band of fibrous tissue, attached by one end to the superior half of the pit or depression on the head of the femur. By its medial end it is attached to the lower edge of the

Anterior inferior articular surface of

iliac spine the transverse ligament, with extensions to the opposite borders of

the acetabular notch,

Labrum glenoidale but chiefly to the posterior or ischial border. This ligament varies very

Pubo-capsular

ligament greatly

its strength and development in different subjects, and in certain rare cases it is absent.

The so-called Haversian gland occupies the bottom or non-articular area of the acetabulum.

Pubo-capsular ligament It consists of a mass of fat covered by the

Fig. 316.-DISSECTION OF THE HIP-JOINT FROM THE FRONT. synovial stratum of the joint. This pad of fat is continuous with the extra-capsular fat through the passage subjacent to the transverse ligament of the acetabulum.

A synovial stratum lines the fibrous stratum of the capsule from which it is reflected to the neck of the femur along a line which corresponds to the femoral attachments of the fibrous stratum. Thus the synovial stratum clothes more of the femoral neck anteriorly than in any other position. Posteriorly, where the fibrous stratum is feebly attached to the neck of the femur, the synovial stratum may be seen from the outside of the capsule. The synovial stratum extends close up to the articular margin of the head of the femur, and on the superior and inferior aspects of the neck it is gathered into loose folds upon the retinacula. These folds or plicæ synoviales are best marked along the line of synovial reflection, and do not reach as far as the femoral head. At its acetabular end the synovial stratum is prolonged from the inside of the capsule to the outer non-articular surface of the labrum glenoidale and transverse ligament, upon which it is continued as a lining for their acetabular or articular surfaces, and further, it

provides a covering for the fat at the bottom of the acetabular fossa, as well as a complete tubular investment for the ligamentum teres femoris.

Occasionally the synovial bursa, which is subjacent to the tendon of the iliopsoas muscle, communicates with the interior of the hip-joint through an opening

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The two portions of the ilio

femoral ligament

Obturator membrane

in the anterior wall of the capsule (Fig. 316), situated between the pubo-capsular ligament and the medial or lower limb of the ilio-femoral ligament.

Movements at the Hip-Joint.—The movements which occur at the hip-joint are those of a multiaxial joint. These are flexion, extension, abduction, adduction, rotation, and circumduction The range of each of these movements is less extensive than in the case of the shoulder-joint, because, at the hip, the freedom of movement is subordinated to that stability which is essential alike for the maintenance of the erect attitude and for locomotion. When standing at rest in the erect attitude the hip-joint occupies the position of extension, and as the weight of the trunk is transmitted in a perpendicular which falls behind the centres of the hip-joints, both the erect attitude and the extended position are maintained to a large extent mechanically, by means of the tension of the ilio-femoral ligament, without sustained muscular action. Moreover, the tension of this ligament is sustained by the pressure of the front of the head and neck of the femur against its synovial surface. In this association of parts it is important to note that the articular cartilage of the femoral head may be, and in certain races is, prolonged to the front of the femoral neck; and further, that the constant friction does not destroy the synovial stratum of the capsule. Again, the same mechanism which preserves the erect attitude prevents an excessive degree of extension or dorsiflexion. In movement forwards, i.e. ventral flexion, the front of the thigh

approximated to the anterior abdominal wall. The amount of this movement depends upon the position of the knee-joint, because when the latter is flexed the thigh may be brought into contact with the abdominal wall, whereas when the knee-joint is straightened (i.e. extended) the tension of the hamstring muscles greatly restricts the amount of flexion at the hip-joint. Abduction and adduction are likewise much more restricted than at the shoulder-joint. Abduction is brought to a close by the tension of the pubo-capsular band and the lower part of the capsule, and, in addition, the upper aspect of the neck of the femur locks against the margin of the acetabulum. Excessive adduction is prevented by the tension of the upper band of the • ilio-femoral ligament and the upper part of the capsule. Rotation or movement in a longitudinal axis may be either medially, i.e. towards the front, or laterally, i.e. toward the back. In the former the movement is brought to a close by the tension of the ischio-capsular ligament and posterior part of the capsule, aided by the muscles on the back of the joint ; in the latterrotation laterally—the chief restraining factor is the lateral or upper limb of the ilio-femoral ligament. The total amount of rotation is probably less than 60°.

Circumduction is only slightly less free than at the shoulder, but it is complicated by the preservation of the balance upon one foot.

The value and influence of the ligamentum teres femoris are not easily estimated, because it may be absent without causing any known interference with the usefulness of the joint. In the erect attitude this ligament lies lax between the lower part of the femoral head and the acetabular fat. In the act of walking it is rendered tense at the moment when the pelvis is balanced on the summit of the supporting femur. Analysis of this position shows the femur to be adducted, with probably, in addition, a small amount of flexion (i.e. bending forwards) and medial rotation. Again, this ligament is said to be tense when the thigh is rotated laterally. The equivalent of this movement is doubtless found in the rotation of the pelvis, which occurs in the act of walking at the moment of transition from the toe of the supporting foot to the heel of the advancing foot. The interest connected with this ligament is perhaps rather morphological than physiological. It is believed by some to represent the tendon of a muscle which in birds occupies a position external to the joint capsule.

ARTICULATIO GENU.

The knee-joint is the largest articulation in the body, and its structure is of a very elaborate nature. The part it plays in maintaining the erect attitude materially influences its construction, and special arrangements are provided for the mechanical retention of the joint in the extended position in view of the fact that the line of gravity falls in front of the centre of the articulation. Its principal axis of movement is in the transverse direction, consequently it belongs to the ginglymus or hinge variety of the diarthroses. At the same time a slight amount of rotation of the tibia in its long axis is permitted during flexion; but while this fact is of considerable importance in the study of certain accidents to which the joint is liable, as well as in the study of its comparative morphology, it is not sufficiently pronounced to interfere with its classification as a hinge-joint.

Articular surfaces pertaining to the femur, tibia, and patella enter into the formation of the knee-joint. The articular surface of the femur extends over a large part of both condyles, and may be divided into patellar and tibial portions by faintly-marked, almost transverse grooves, which pass across the articular surface immediately in front of the intercondylar notch. As a rule marginal indentations of the articular surface render the positions of these transverse grooves more distinct.

The patellar portion (Fig. 317) is situated anteriorly, and is common to both condyles, although developed to a larger extent in association with the lateral condyle, on which it ascends to a more proximal level than on the medial condyle. This surface is trochlear, and forms a vertical groove bordered by prominent borders.

The tibial portion of the articular surface of the femur is divided into two articular areas, in relation to the distal aspects of the two condyles, by the wide non-articular intercondyloid notch. These two surfaces are for the most part parallel, but in front the medial tibial surface turns obliquely laterally as it passes into continuity with the patellar trochlea, while posteriorly, under certain circumstances, e.g. the squatting posture, the articular surface of the medial condyle may extend to the adjoining portion of the popliteal area of the bone.

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Fig. 317.-DISSECTION OF THE KNEE-JOINT FROM THE FRONT : PATELLA THROWN DISTALLY.

When the joint is in the position of extreme flexion, the patella is brought into direct contact with that part of the articular surface on the medial condyle which bounds the intercondyloid notch upon its medial and anterior aspects. This relationship is indicated by the presence of a distinct semilunar facet on the cartilage in that situation (Fig. 317). The articular surface of the femur may therefore be regarded as presenting femoro-patellar and femoro-tibial areas.

The patella presents 'on its posterior aspect a transversely elongated oval articular facet and a distal rough, triangular, non-articular area. The articular facet is divided into two principal portions by a prominent rounded vertical ridge. Of these the lateral is the wider. A less pronounced and nearly vertical ridge marks off an additional facet called the medial perpendicular facet, close to the medial margin of the articular surface. Two faint transverse ridges cut off narrow proximal and distal facets from the general articular surface without encroaching on the narrow, most medial vertical facet (Goodsir) (Fig. 317).

The head of the tibia presents on its superior aspect two condylar articular surfaces, separated from each other by a non-articular antero-posterior area, which is wider anteriorly and posteriorly than in the middle, where it is elevated to form a bifid eminentia intercondyloidea.

The lateral condylar facet is slightly concavo-convex from before backwards

and slightly concave transversely. This surface is almost circular, and extends to the free lateral border of the tibial condyle, where it is somewhat flattened. Posteriorly the articular surface is prolonged downwards on the condyle in relation to the position occupied by the tendon of the popliteus muscle. The medial condylar facet is oval in outline, and distinctly concave both in its anteroposterior and transverse diameters.

Ligaments.—Like all diarthroses, this joint is invested by an envelope or capsula articularis, which does not, however, entirely surround the articular cavity, for it is absent as a fibrous stratum proximal to the articular cavity, subjacent to the tendon of the quadriceps extensor muscle. Its specially named bands are not

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of themselves sufficient to form a complete investment, and the fibrous stratum, which largely consists of augmentations from the fascia lata and the tendons of surrounding muscles, supplies the defective areas. Thus, anteriorly, on each side of the patella and the ligamentum patellæ, expansions of the vasti tendons and fascia lata, constituting the collateral patellar ligaments, are evident. On the lateral side of the joint the fibular collateral ligament is hidden within a covering derived from the ilio-tibial tract of the fascia lata. On the medial side expansions from the tendons of the sartorius and semi-membranosus muscles augment the articular capsule, which here becomes continuous with the ligamentum collaterale tibiale. Posteriorly the articular capsule also receives augmentation from the tendon of the semi-membranosus muscle, but it is very thin subjacent to the origins of the gastrocnemius muscle, where it covers the posterior parts of the condyles. Not unfrequently the articular capsule presents an opening of communication between

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