pages 333

</TR

each is attached by one extremity to the posterior tubercle and adjacent depression on the side of the head of the metacarpal bone, and by the other to the contiguous extremity of the phalanx.

The dorsal surfaces of these joints are covered by the expansions of the Extensor tendons, together with some loose areolar tissue which connects the deep surfaces of the tendons to the bones.

Movements.—The movements which occur in these joints are flexion, extension, adduction, abduction, and circumduction; the movements of abduction and adduction are very limited, and cannot be performed when the fingers are flexed.

6k. Articulations of the Digits

(Articulationes Digitorum Manus; Interphalangeal Joints) (Figs. 337, 338)

The interphalangeal articulations are hinge-joints; each has a volar and two collateral ligaments. The arrangement of these ligaments is similar to those in the metacarpophalangeal articulations. The Extensor tendons supply the place of posterior ligaments.

Movements.—The only movements permitted in the interphalangeal joints are flexion and extension; these movements are more extensive between the first and second phalanges than between the second and third. The amount of flexion is very considerable, but extension is limited by the volar and collateral ligaments.

Muscles Acting on the Joints of the Digits.—Flexion of the metacarpophalangeal joints of the fingers is effected by the Flexores digitorum sublimis and profundus, Lumbricales, and Interossei, assisted in the case of the little finger by the Flexor digiti quinti brevis. Extension is produced by the Extensor digitorum communis, Extensor indicis proprius, and Extensor digiti quinti proprius.

Flexion of the interphalangeal joints of the fingers is accomplished by the Flexor digitorum profundus acting on the proximal and distal joints and by the Flexor digitorum sublimis acting on the proximal joints. Extension is effected mainly by the Lumbricales and Interossei, the long Extensors having little or no action upon these joints.

Flexion of the metacarpophalangeal joint of the thumb is effected by the Flexores pollicis longus and brevis; extension by the Extensores pollicis longus and brevis. Flexion of the interphalangeal joint is accomplished by the Flexor pollicis longus, and extension by the Extensor pollicis longus.

7. Articulations of the Lower Extremity. a. Coxal Articulation or Hip-joint

The articulations of the Lower Extremity comprise the following:

I. Hip.		V. Intertarsal.
II. Knee.		VI. Tarsometatarsal.
III. Tibiofibular.		VII. Intermetatarsal.
IV. Ankle.		VIII. Metatarsophalangeal.
IX. Articulations of the Digits.

Coxal Articulation or Hip-joint (Articulatio Coxæ)

This articulation is an enarthrodial or ball-and-socket joint, formed by the reception of the head of the femur into the cup-shaped cavity of the acetabulum. The articular cartilage on the head of the femur, thicker at the center than at the circumference, covers the entire surface with the exception of the fovea capitis femoris, to which the ligamentum teres is attached; that on the acetabulum forms an incomplete marginal ring, the lunate surface. Within the lunate surface there is a circular depression devoid of cartilage, occupied in the fresh state by a mass of fat, covered by synovial membrane. The ligaments of the joint are:

The Articular Capsule.		The Pubocapsular.
The Iliofemoral.		The Ligamentum Teres Femoris.
The Ischiocapsular.		The Glenoidal Labrum.
The Transverse Acetabular

Contents -SUBJECT INDEX -BIBLIOGRAPHIC RECORD -ILLUSTRATION INDEX