its formation. The lowest arch lies on the tibia immediately above its tubercle, and results from the anastomosis of the recurrent tibial and inferior internal articular arteries. The upper and middle of these transverse arches are connected, on each side of the patella, by ascending and descending branches, which anastomose with one another, and thus enclose the patella in an irregularly quadrilateral arterial framework. From all sides of this arterial enclosure, twigs are given off which enter small foramina on the anterior surface of the patella to supply the osseous substance. Six arteries therefore take part in the formation of this system of anastomoses, on the front and lateral aspects of the joint, viz., the deep branch of the anastomotica, the two superior and the two inferior articular branches of the popliteal and the anterior recurrent branch of the anterior tibial. In addition to the twigs which proceed from these to form the arterial arches, numerous branches are given which spread over the bones in the form of a close meshwork. During the dissection of the articulation these vessels will become apparent.

The knee-joint is supplied on its posterior aspect by twigs derived from all the articular branches of the popliteal. These twigs are variable in their origin, and the anastomoses which are formed between them are unimportant and inconstant. They are sometimes supplemented by another artery, the posterior recurrent tibial. This small vessel is a branch of the anterior tibial before it leaves the back of the leg. It ascends under cover of the popliteus muscle, ramifies over the lower part of the ligamentum posticum Winslowii, and inosculates with the two inferior articular branches of the popliteal.

The azygos articular artery is chiefly destined for the supply of the interior of the joint. It pierces the posterior ligament, passes forwards between the crucial ligaments, and ramifies in the fatty tissue in that situation. Its terminal twigs usually anastomose with the intermediate arch in front of the knee-joint. It will be dissected at a later stage in the interior of the joint.

Articular Nerves. The knee-joint is richly supplied No less than ten distinct branches may be The anterior crural, the external popliteal,

with nerves. traced to it.

and the internal popliteal trunks, contribute three twigs apiece to this articulation, and the obturator furnishes a filament to its posterior aspect. The anterior crural supplies the joint through branches which proceed from the nerves to the vastus externus, vastus internus, and subcrureus. These nerves pierce the fibres of the quadriceps muscle, and are distributed to the upper and anterior part of the articulation. The articular branch from the nerve to the vastus internus is of larger size than the other two, and it accompanies the deep branch of the anastomotic artery. The external popliteal nerve gives off-(1) the superior and inferior external articular nerves: these accompany the arteries of the same name, and end in fine filaments, which pierce the capsule of the joint; and (2) the recurrent articular nerve which accompanies the anterior recurrent tibial artery. This nerve ends chiefly in the tibialis anticus muscle; but a fine twig may reach the lower part of the anterior aspect of the knee-joint. The internal popliteal nerve furnishes the knee-joint with superior and inferior internal articular and azygos articular nerves, which accompany the arteries of the same name. The branch from the obturator nerve descends on the posterior aspect of the popliteal artery as far as the back of the knee-joint. At this point it leaves the artery and, inclining forwards, breaks up into several filaments which separately pierce the posterior ligament.

ARTICULATIONS.

The dissection of the knee-joint, the ankle-joint, the tibio-fibular joints, and the various articulations of the foot, may now be proceeded with. It is possible that the ligaments may have become hard and dry. If this be the case, soak the joints in water for an hour or two.

Knee-joint (articulatio genu).-In this joint three bones. are in apposition, viz., the lower end of the femur, the

upper end of the tibia, and the patella. It is the largest and most complicated articulation in the body; and if the bones be examined in the skeleton, the joint presents an apparent insecurity, because the bony surfaces show little adaptation the one to the other. In reality, however, it is very strong, and very rarely suffers dislocation on account of the strength of the ligaments which retain the bones in place. The ligaments on the exterior of the knee-joint are:

1. The capsular ligament.

2. Two lateral ligaments-external and internal.
3. The ligamentum patellæ (or anterior ligament).
4. The posterior ligament.

Dissection. The popliteal vessels and nerves, and the muscles surrounding the knee-joint, must be removed. Portions of the tendons of the biceps, semimembranosus, sartorius, semitendinosus, gracilis, and popliteus, together with small pieces of the heads of the gastrocnemius, should be left in place in order that their connection with the ligaments of the joint may be studied. The quadriceps extensor may be divided about three inches above the patella, and the lower part allowed to remain in position. Further, the various articular arteries which surround the joint should be followed to their terminations.

The Capsule (capsula articularis) of the knee-joint, together with the internal and posterior ligaments, form a complete investment for the articulation. In the upper and front part of the joint it is deficient, but here its place is taken by the common tendon of the quadriceps extensor muscle. The capsule may be regarded as an aponeurotic expansion on the front of the articulation, which fills up the intervals between the two lateral and the anterior ligaments. The fascia lata and expansions from the surrounding tendons enter into its formation. Thus, on the outer aspect, it is largely composed of the ilio-tibial band of fascia lata as this proceeds downwards to its attachment to the tibia. Traced backwards, the capsule will be seen to be prolonged over, and to hide from view, the external lateral ligament. On the inner side of the limb it receives expansions from the sartorius

and semimembranosus, and fuses with the internal lateral ligament.

The Ligamentum Patellæ forms the anterior ligament of the knee-joint, and constitutes, at the same time, the tendon of insertion of the quadriceps extensor muscle. By the removal of the capsular expansion from its surface it may be fully exposed and its margins defined.

The ligamentum patella is a strong band, about two inches long, which is attached above to the apex and lower border of the patella, and below to the lower part of the anterior tubercle of the tibia. Its superficial fibres are directly continuous over the surface of the patella with the central part of the common tendon of the quadriceps extensor. Its deep surface rests upon the infrapatellar pad of synovial fat, and upon a small bursa which intervenes between it and the upper part of the anterior tubercle of the tibia. The two lower arterial anastomotic arches of the knee are placed under cover of it.

Dissection. The external lateral ligament may be exposed by removing the part of the capsule which is formed by the ilio-tibial band of fascia lata, and also the prolongation which this gives backwards over the ligament. By this proceeding the inferior external articular artery will be displayed as it extends forwards to the front of the joint.

The External Lateral Ligament (ligamentum collaterale fibulare) is rounded and cord-like. It stands well away from the joint, and is attached above to a tubercle on the outer tuberosity of the femur. Below, it is fixed to a depression on the head of the fibula in front of the styloid process. It is closely associated with the tendon of the biceps and the tendon of the popliteus. It splits the tendon of the biceps into two pieces, and extends vertically downwards to its fibular attachment between them. The tendon of the popliteus takes origin from the outer tuberosity of the femur below and in front of the femoral attachment of the external lateral ligament. As the tendon proceeds backwards it is placed under cover of the ligament.

An additional slip is sometimes described as the posterior part of the external lateral ligament. When present it is attached to the femur, under cover of the outer head of the gastrocnemius, in connection with the posterior ligament. Below, it is implanted into the styloid process

of the fibula.

The Internal Lateral Ligament (ligamentum collaterale tibiale) is a long flat band, broader in the middle than at either extremity, which springs from the inner tuberosity of the femur below the adductor tubercle. As it descends it inclines slightly forwards, and finally it gains attachment to the upper part of the shaft of the tibia below the internal tuberosity. The main part of the tendon of the semimembranosus extends forwards under cover of its posterior border to gain an insertion into the tuberosity of the tibia, whilst lower down the inferior internal articular vessels are carried forwards between it and the bone. The tendons of the sartorius, gracilis, and semitendinosus, lie upon its superficial surface, but are separated from it by an intervening bursa.

The Posterior Ligament stretches from the external to the internal lateral ligament. Above, it is fixed to the upper margin of the intercondyloid notch, whilst on either side it becomes incorporated with the corresponding head of the gastrocnemius. Below, it is attached to the posterior border of the upper end of the tibia. A strong slip derived from the tendon of the semimembranosus strengthens the ligament on its posterior aspect. This band passes upwards and outwards towards the external condyle of the femur.

Sometimes the term "posterior ligament" (ligamentum posticum Winslowii) is restricted to this oblique band from the semimembranosus, and the remainder of the ligament as described above is then regarded as a portion of the capsule.

The posterior ligament presents a number of apertures for the entrance of blood-vessels and nerves into the interior of the joint. The azygos artery is the most conspicuous of these vessels. An opening may likewise sometimes be observed over the upper part of the internal condyle of the femur. Through this protrudes a pouch of synovial membrane which forms a bursa under the inner head of the gastrocnemius. As a rule, however, this bursa is independent of the knee