membrane, while the lower has been already used as an example of a syndesmosis or fibrous half joint. The ANKLE JOINT is a hinge, the astragalus being received into a lateral arch formed by the- lower ends of the tibia and fibula. Backward dislocation is prevented by the articular surface of the astragalus being broader in front than behind. The anterior and posterior parts of the capsule are feeble, but the lateral ligaments are very strong, the external consisting of three separate fasciculi which bind the flbula to the astragalus and calcaneum. To avoid confusion it is best to speak of the movements of the ankle as dorsal and plantar flexion. The tarsat joints resemble the carpal in being gliding articulations. There are two between the astragalus and calcaneum, and at these inversion and eversion of the foot largely occur. The inner arch of the foot is maintained by a very important ligament called the catcaneo-naoicular or spring ligament; it connects the sustentaculum tali of the calcaneum with the navicular, and upon it the head of the astragalus rests. When it becomes stretched, flat-foot results. The tarsal bones are connected by dorsal, plantar and

interosseous ligaments.

The long

and short calcaneocuboid

are plantar

ligaments of special

importance, and

maintain the outer

arch of the foot.

The tarso-metatarsal,

m eta ta r s 0plzalangeal

and in-

terphalangeat joints

closely resemble

those of the hand,

except that the

ta1'S0- IT1 6 t 3. t 3. I' S al Anterior superior tibio-fibular joint of the great l'g”""'“'t

toe is not saddle shaped.

Impression of extem

lunar

External tibial surface of

femur

External lateral ligament,

Cut tendon of biceps flexor

cruris muscle

External lateral

Comparative Anatomy.~The

anterior

fasciculus of the external

lateral ligament

of the ankle is

only found in Man,

and is probably an

adaptation to the

erect position. In

anima s with a long

foot, such as the

Ungulates and the

Kangaroo, the lateral

ligaments of the

ankle are in the form of an X, to give greater protection against lateral movement. In certain marsupials a libro-cartilage is developed between the external malleolus and the astragalus, and its origin from the deeper fibres of the external lateral ligament of the ankle can be traced. These animals have a rotatory movement of the flbula on its long axis, in addition to the hinge movement'of the ankle. For further details of joints see R. Fick, Handbuch der Gelenke (jena, 1904); H. Morris, Anatomy of the Joints (London, 1879); Quain's, Gray's and Cunningham's Text-books of Anatomy; ]. Bland Sutton, Ligaments, their Nature and Morphology (London, 1902); F. G. Parsons, “ Hunterian Lectures on the joints of Mammals, ” Journ. Anat. fs' Phys., xxxiv. 41 and 301. (F. G. P.) Opening in

membrane for

(From D. Hepburn, Cunningham's Text-book of Anatomy.) DISEASES AND INJURIES or IOINTS The affection of the joints of the human body by specific diseases is dealt with under various headings (RHEUMATISM, &c.); in the present article the more direct forms of ailment are discussed. In most joint-diseases the trouble starts either in the synovial lining or in the bone-rarely in the articular cartilage or ligaments. As a rule, the disease begins after an injury. There are three principal types of injury: (1) sprain or strain, in which the ligamentous and tendinous structures are stretched or lacerated; f 2) contusion, in which the opposing bones are

FIG. 7.-Dissection of the Knee-joint from the front: Patella thrown down.

driven forcibly together; (3) dislocation, in which the articular surfaces are separated from one another. A sprain or strain of a joint means that as the result of violence the ligaments holding the bones together have been suddenly stretched or even torn. On the inner aspect the ligaments are lined by a synovial membrane, so when the ligaments are stretched the synovial membrane is necessarily damaged. Small blood-vessels are also torn, and bleeding occurs into the joint, which may become full and distended. If, however, bleeding does not take place, the swelling is not immediate, but synovitis having been set up, serous effusion comes on sooner or later. There is often a good -deal of heat of the surrounding skin and of pain accompanying the synovitis. In the case of a healthy individual the effects of a sprain may quickly pass off, but in a rheumatic or gouty person chronic synovitis may obstinately remain. In a person with a tuberculous history, or of tuberculous descent, a sprain is apt to be the beginning of serious disease of the joint, and it should, therefore, be treated with continuous rest and prolonged supervision. In a person of health and vigour, a sprained joint should be at once bandaged. This may be the only treatment needed. It gives support and comfort, and the even pressure around the joint checks ellusion into it. Wide pieces of adhesive strapping, layer on layer, form a still more useful support, and with the joint so treated the person may be able at once to use the limb. If strapping

is not employed,

the bandage may be

taken off from time

to time in order that

the limb and the

joint may be massaged.

If the sprain

is followed by much

synovitis a plaster of

Paris or leather splint

may be applied, complete

rest being secured

for the limb.

Later on, blistering

or even “ firing "

may be found advisable.

Synovitis. -When

a joint has been injured,

inflammation

occurs in the damaged

tissue; that is inevitable.

But sometimes

the attack of inflammation

is so slight

and transitory as to

be scarcely noticeable.

This is specially

likely to occur if the

joint-tissues were in

a state of perfect

nutrition at the time

of thehurt. Butifthe

individual or the joint

were at that time in

a state of imperfect

nutrition, the effects

are likely to be more

serious. Asarule, it is

the synovial membrane lining the fibrous capsule of the joint which first and chiefly suffers; the condition is termed synovitis. Synovitis may, however, be due to other causes than mechanical injury, as when the interior of the joint is attacked by the micro-organisms of pyaemia (blood-poisoning), typhoid fever, pneumonia, rheumatism, gonorrhoea or syphilis. Under judicious treatment the synovitis generally clears up, but it may linger on and cause the formation of adhesion's which may temporarily stiffen the joint; or it may, especially in tuberculous, septic or pyaemic infections, involve the cartilages, ligaments and bones in such serious changes as to destroy the joint, and possibly call for resection or amputation. The symptoms of synovitis include stiffness and tenderness in the joint. The patient notices that movements cause pain. Effusion of fluid takes place, and there is marked fullness in the neighbourhood. If the inflammation is advancing, the skin over the joint may be flushed, and if the hand is placed on the skin it feels hot. Especially is this the case if the joint is near the surface, as at the knee, wrist or ankle.

The treatment of an inflamed joint demands rest. This may be conveniently obtained by the use of a light wooden s lint, padding and bandages. Slight compression of the joint by a bandage is useful in promoting absorption of the fluid. If the inflamed joint is in the lower extremity, the patient had best remain in bed, or on the sofa; if in the upper extremity, he should wear his arm in a sling. The muscles acting on the joint must be kept in complete control. If the inflammation is extremely acute, / Patellar surface of femur

qemilunar facet for patella

nal tibial surface of

crucial ligament

crucial ligament

Transverse ligament

semi lunar fibro-Internal

lateral ligament

- -Ligamentum patellm

perpendicular facet on