of the external head of the gastrocnemius, and the upper attachment of the external lateral ligament; it passes downwards and backwards beneath the external lateral ligament, and behind the outer part of the articulation, to the upper part of the tibia, into the posterior surface of which it is inserted, above an oblique ridge named the linea poplitei. Its tendon is connected to the external semilunar cartilage by ligamentous fibres, and also to the synovial membrane, by which it is partly surrounded, and through which connection a communication is sometimes found to exist between the articulation of the fibula with the tibia, and the knee-joint. The action of the popliteus is to assist the hamstring muscles in flexing the leg on the thigh; or it may flex the thigh on the leg; it may also rotate the tibia slightly, or the femur when the tibia is fixed. By its connection with the semilunar cartilage, it may fix it in its proper place.

The FLEXOR LONGUS DIGITORUM COMMUNIS PEDIS, Fig. 241 (1), arises from the posterior surface of the tibia, commencing just below the insertion of the popliteus and the origin of the soleus, and extending down to within three or four inches of the ankle; it also has some fibres arising from the aponeurosis on the tibialis posticus, and from intermuscular septa. From this origin the fibres pass obliquely backwards and inwards, to end in a tendon which descends to a groove behind the internal malleolus, where it is covered and fixed in its place by the internal annular ligament, and separated from the tendon of the tibialis posticus by a process of the annular ligament. It is surrounded by a synovial membrane which extends some distance above and below the groove. From this point it is directed forwards and a little. outwards, to pass through a groove in the astragalus, and also one in the os calcis, when it enters the sole of the foot, where it is first joined by a slip from the tendon of the flexor longus pollicis, and next by the musculus accessorius; it now divides into four tendons, one for each of the four smaller toes. Each tendon passes through a fibrous sheath lined by synovial membrane. This sheath corresponds to the under surface of the first and second row of phalanges. Each contains also one of the tendons of the flexor brevis digitorum communis, each of which is slit opposite the base of the second phalangeal bone, for the transmission of the corresponding tendon

of the long flexor, as it passes forwards, to be inserted into the base of the last phalangeal bone.

Fig. 241.

The FLEXOR LONGUS POLLICIS PEDIS, Fig. 241 (9), is placed to the outer side of the preceding muscle, from which it is partly separated by the tibialis posticus. It arises from the lower two-thirds of the fibula, from the aponeurosis which covers the tibialis posticus, and from the interosseous membrane near the lower end of the fibula, and also from a fibrous septum between it and the peronei muscles. The fibres pass obliquely downwards and inwards, to end in a tendon which descends to a groove first on the inner side of the astragalus, and then of the os calcis, being kept by a strong fibrous sheath, firmly applied to these bones; from this point it is continued into the sole of the foot, and through it to the base of the last phalangeal bone of the great toe, into which it is inserted. Its tendon crosses above that of the long common flexor of the toes, and gives to it a tendinous slip; in the latter part of its course, it is placed between the bellies of the short flexor of the great toe. Opposite the internal malleolus, it is separated from the tendon of the long common flexor of the toes and the tendon of the tibialis posticus, by the posterior tibial vessels and nerve. The peroneal vessels are placed between its origin from the fibula, and its origin from the aponeurosis on the inner side of that bone. Its tendon passes very nearly through the whole muscle. Its action is to flex the great toe, and, having

14

THE DEEP LAYER OF MUSCLES OF THE POSTERIOR TIBIAL REGION OF THE LEFT LEG.-1. The lower extremity of the femur. 2. The ligamentum posticum Winslowii. 3. The tendon of the semi-membranosus muscle dividing into its three slips. 4. The internal lateral ligament of the knee-joint. 5. The long external lateral ligament. 6. The popliteus muscle. 7. The flexor longus digitorum. 8. The tibialis posticus. 9. The flexor longus pollicis. 10. The peroneus longus muscle. 11. The peroneus brevis. 12. The tendo-Achillis divided near its insertion into the os calcis. 13. The tendons of the tibialis posticus and flexor longus digitorum muscles, just as they are about to pass beneath the internal annular ligament (14) of the ankle; the interval between the latter tendon and the tendon of the flexor longus pollicis is occupied by the posterior tibial vessels and nerve.

done this, to extend the foot on the leg, and to adduct the foot.

The TIBIALIS POSTICUS, Fig. 241 (8), is situated in the middle of the interosseous fossa, or rather occupies a large portion of it, except at the lower part, where it has become tendinous. It arises from both bones of the leg, and from the interosseous membrane; from the fibula, it arises between the origin of the soleus muscle and the outer malleolus, from the tibia, below the linea poplitei, and from nearly the whole of the posterior surface of the interosseous membrane; it also arises from the intermuscular septa, which separate it from the two preceding muscles. The fibres, which arise from these different points, pass downwards to end in a tendon which extends nearly the whole length of the muscle, occupying the central part of it. This tendon passes between that of the flexor longus digitorum communis and the tibia, to get into a fibrous canal above and behind the internal malleolus, and to the inner side of the tendon of the lastnamed muscle; it then continues obliquely forwards and is inserted into the scaphoid and the internal and middle cuneiform bones; sometimes some fibres can be traced from it to the base of the metatarsal bone of the great toe, and also to the external cuneiform bone. A sesamoid bone, or fibrocartilage, is very frequently found in its tendon just behind its insertion into the scaphoid bone. A synovial membrane is placed between this sesamoid body and the scaphoid bone. The upper end of the muscle is notched for the passage of the anterior tibial vessels. Its action is to extend the foot on the leg; it will also invert the plantar surface of the foot by elevating its inner border; with the long flexor muscles of the toes it may act as a substitute for the gastrocnemius and soleus in case the tendo-Achillis has been injured. It also assists in steadying the foot in standing or walking.

Having completed the dissection of the back of the leg, the student should review what he has been over, including in this review the popliteal space. He should carefully examine the deep fascia to see in what manner they would limit or favor in any particular direction, the extension of collections of pus. He will notice that pus, collected beneath the deep fascia of the popliteal space, might extend to the foot without encountering any obstruction from fascia; and also that in en

tering the leg it would pass down in the sheath of the superficial layer of muscles; or, if it should form beneath the fascia which covers the deep layer of muscles, it might pass under the internal annular ligament and enter the sole of the foot. Thus it will be seen that the cavity formed by the sheath of the superficial layer of muscles communicates with that formed by the fascia lata of the thigh, while that formed by the sheath of the deep layer communicates with that formed by the plantar aponeurosis.

He should examine the different arteries of this region, and study their relations to prominent points which can always be seen or felt in the living subject, and by which he will be enabled at any time to locate any one of these vessels; and also, such points as will serve for guides in finding either one of the arteries in case he should ever have occasion to ligate them in his practice. Take, for example, the posterior tibial artery two or three inches below its origin; he should carefully examine its relations to the gastrocnemius and soleus muscles, in order to determine whether it could. be reached better by cutting directly upon it through those muscles, or by detaching the soleus from the tibia or fibula, and then following the fascia which separates the superficial from the deep layer of muscles. He has already seen in the dissection of these parts that this fascia covered the artery; he has also seen the position of the nerve, so that he would be able to take this into consideration in deciding the best way to reach the artery without injuring the nerve. He should likewise study the relations of the same artery lower down; and, also, the peroneal artery. The position of the tendons of the long muscles of the foot as they pass through the sulcus formed, on the inner side by the internal malleolus, and on the outer side by the tendo-Achillis and the os calcis, should receive special attention. It may happen to him some time that he will have occasion to divide one or more of these tendons. A short time devoted to the study of these parts, now they are before him, may prove to be of immense use to him at some future time, and he cannot neglect this opportunity to acquire this knowledge without doing himself great injustice, as well as those who will have a right to demand of him the application of it to themselves.

SECT. V.-DISSECTION OF THE ANTERIOR AND OUTER PARTS OF THE LEG, AND THE DORSUM OF THE FOOT.

As there is so little on the dorsum of the foot that is not found on the leg, while almost every thing to be dissected on the leg, such as fascia, muscles, vessels, and nerves, not only extend to, but pass over the dorsum of the foot, we think it is better to make but one dissection of these regions. Nor is the number of the parts to be examined so great that the student cannot, if proper means be employed to preserve the subject from drying or decomposing, dissect them in a satis factory manner while they are in a suitable condition for this purpose. There is, perhaps, more danger to be apprehended from the parts drying and becoming hard on the foot, than of their decomposing, especially if a strong solution of chloride of zinc has been used as an antiseptic; this can be prevented only by the constant use of wet-cloths kept applied to the limb during the intervals of dissecting. The foot should be extended on the leg, and kept in this position by means of hooks; in dissecting the muscles it will be neces sary, not only to extend the foot, but to abduct it in dissecting the tibialis anticus, and adduct it in exposing the pe ronei muscles.

To remove the integument a vertical incision may be made, commencing at the knee and extending it down the leg a little to the outside of the spine of the tibia to the anklejoint, and thence in a straight line on the dorsum of the foot to the space between the great and the second toe. Two transverse incisions should be made; an upper one extending from the ligamentum patella to the outer hamstring, and a lower one from one malleolus to the other in front of the ankle-joint. If the thigh and back part of the leg have already been dissected, it may not be necessary to make any new incisions, or it may be more convenient to make them in a different manner; the student will have no difficulty in determining the most convenient way, when he remembers that the manner in which the skin is removed has nothing to do with the dissection of the parts beneath it, except to get it out of the way as fast as, but no faster than is required to expose those parts, and to use it for covering them when he is not dissecting. Care is necessary here as well as elsewhere in