Part 19

_Insertion_ of which is into the medial surface of the femur on the medial epicondyle, at the middle of its distal border and into the adjacent medial surface of the tibia behind the lateral ligament.

The dorsal part has its _insertion_ into the distal one and one-half to two centimeters of the ridge which is continued from the medial epicondyle of the femur onto the shaft; and into the sesamoid bone of the medial epicondyle.

_Relations._--Lateral surface with the semitendinosus (Fig. 90, _j_), the biceps femoris (Fig. 68, _t_), and distad with a small part of the adductor femoris (Fig. 92, _g_), and with the gastrocnemius (Fig. 92, _j_). Medial surface with the gracilis (Fig. 91, _b_) and distad with the sartorius (Fig. 91, _a_). Cranial (or dorsal) border at the origin with the quadratus femoris (Fig. 90, _f_); for the remainder of its length with the adductor femoris (Fig. 90, _h_). Caudal border with the integument proximad.

_Action._--Extensor of the thigh.

=M. sartorius= (Fig. 91, _a_; Fig. 68, _q_).--A large flat muscle along the medial side of the thigh near its cranial (dorsal) border.

_Origin_ from the ventral half of the crest of the ilium and from the medial half of its ventral border craniad of the auricular impression. The caudal third of the origin is by a thin tendon, the rest by fleshy fibres.

_Insertion_ on a long S-shaped line which begins on the dorsal border of the tibial shaft about two centimeters from its proximal end, passes thence to the middle of the proximal end of the medial surface of the tibia, thence across the ligaments of the knee-joint and the medial surface of the medial epicondyle to the patella, crosses the patella obliquely to the middle of its proximal end, and may be continued for some distance proximad along the middle line on the fascia.

_Relations._--Medial surface with the integument and proximad with the internal oblique muscle (Fig. 68, _p_). Lateral (inner) surface with the tensor fasciæ latæ (Fig. 68, _r_), the vastus lateralis (Fig. 90, _d_), the superficial fascia, the vastus medialis (Fig. 92, _c_), the rectus femoris (Fig. 92, _b_), and the distal end of the semimembranosus (Fig. 92, _h′_).

_Action._--Adducts and rotates the femur and extends the tibia.

=M. gracilis= (Fig. 91, _b_).--The gracilis is a flat, thin, subcutaneous muscle occupying the ventral half of the medial surface of the thigh.

_Origin_ by a strong tendon from the caudal three-fourths of the symphysis of the ischium and pubis. The tendon may extend caudad of the symphysis in the middle line to the level of the tuberosity of the ischium. For about its first centimeter the tendon is common to the two muscles of opposite sides and gives origin on two sides to the fibres of the adductor femoris. The common tendon divides into two which pass laterad, each ending in a convex border from which the muscle-fibres spring.

_Insertion._--It ends in a thin aponeurosis, part of which is continuous with that of the sartorius. The aponeurosis is finally inserted into the medial surface of the tibia near its proximal end, while distally it is continuous with the fascia.

_Relations._--Outer (medial) surface with the integument. Inner (lateral) surface with the semimembranosus (Fig. 91, _i_) and the adductor femoris (Fig. 91, _h_).

_Action._--Adducts the leg and draws it caudad.

=M. adductor femoris= (magnus et brevis) (Fig. 92, _g_; Fig. 90, _h_).--The adductor femoris lies between the semimembranosus (Fig. 92, _h_) and the femur. Its proximal part is covered by the semimembranosus, while its distal part lies outside of it.

_Origin_ by muscle-fibres from the rami of the pubis and the ischium along the whole of the length of the symphysis; from the ramus of the ischium between the symphysis and the tuberosity, and from the tendon of origin common to the two gracilis muscles.

_Insertion_ into nearly the whole of the ventral surface of the shaft of the femur. The area begins at the base of the great trochanter opposite the proximal end and the insertion area of the gluteus maximus. It extends thence distad along the caudal border of the surface as an area about one millimeter wide. At the junction of the first and second thirds of the shaft the area expands and occupies the whole of the ventral surface of the bone, ending at the intercondyloid fossa.

_Relations._--Lateral surface with the biceps (Fig. 68, _t_), the great sciatic nerve (Fig. 163, _a_), the tenuissimus (Fig. 90, _g_), and the semimembranosus (Fig. 92, _h_); dorsolateral border in contact with the vastus lateralis (Fig. 92, _c_). Dorsal surface with the quadratus femoris (Fig. 90, _f_) and obturator externus (Fig. 90, _e_). Caudal surface with the semimembranosus (Fig. 92, _h_). Medial surface with the gracilis (Fig. 91, _b_), adductor longus (Fig. 92, _f_), pectineus (Fig. 92, _e_), vastus medialis (Fig. 92, _c_), and distad with the medial head of the gastrocnemius (Fig. 92, _j_).

_Action._--An extensor of the thigh.

=M. adductor longus= (Fig. 91, _g_; Fig. 92, _f_).--A thin muscle which covers the dorsal half of the medial surface of the adductor femoris (Fig. 92, _g_).

_Origin_ by muscle-fibres from the median three-fourths of the cranial border of the pubis, the line of origin forming a medial continuation of that of the pectineus (Fig. 92, _e_).

_Insertion_ by a thin aponeurosis into the external linea aspera of the femur along the second and third fifths of the bone.

_Relations._--With its medial or cranial surface the adductor longus forms part of the boundary of a depression among the muscles at the proximal end of the medial side of the leg. This depression is called the iliopectineal fossa; it contains the femoral vein and artery and saphenous nerve imbedded in fat (Fig. 127). The medial edge of the adductor longus is in relation with the integument; the lateral edge with the pectineus (Fig. 92, _e_). Inner or caudal surface with the adductor femoris (Fig. 92, _g_).

_Action._--Adductor of the thigh.

=M. pectineus= (Fig. 92, _e_).--A flat band of fibres closely united with the adductor longus (_f_), of which it appears to be a lateral continuation.

_Origin_ by fleshy fibres from the lateral one-fourth of the cranial border of the pubis. The muscle passes over the smooth outer surface of the pubis between its origin area and the acetabulum, crosses the iliopsoas (_d_) obliquely and has its

_Insertion_ by muscle-fibres into an elongated area (five millimeters in length) on the shaft of the femur just distad of the lesser trochanter and between the insertion of the adductor femoris (_g_) and that of the vastus medialis (_c_).

_Relations._--The cranial edge forms part of the floor of the iliopectineal fossa. Lateral surface in relation with the iliopsoas (_d_) and vastus medialis (_c_); medial surface with the adductor longus (_f_) and adductor femoris (_g_).

_Action._--Adductor of the thigh.

=M. quadriceps femoris.=--The quadriceps femoris is a very powerful extensor muscle on the front of the thigh. It consists of four muscles which unite to form the great extensor of the shank. It is inserted into the patella and through it, by the ligamentum patellæ, into the tibia. It may be compared to the triceps brachii. The parts are:

(1) =M. rectus femoris= (Fig. 92, _b_; Fig. 90, _c_).

_Origin_ by strong tendon from an elongated triangular area which has its base at the acetabulum and its apex about five to seven millimeters craniad of the acetabulum, along the ventral border of the ilium. The area is between that for the capsularis and that for the iliopsoas. The muscle is flat near its origin, but soon becomes a triangular prismatic mass which is united to the dorsal border of the vastus lateralis (Fig. 90, _d_) at the junction of the middle and last thirds of the thigh.

_Insertion_ into the oblique area on the outer surface of the patella near its proximal border in connection with the vastus lateralis.

_Relations._--Outer or lateral surface at the origin with the gluteus minimus, the edge of the capsularis, the gluteus medius (Fig. 90, _b_), and farther distad with the vastus lateralis (Fig. 90, _d_). Medial surface with the tensor fasciæ latæ (Fig. 92, _a_), sartorius (Fig. 90, _a_), and vastus medialis (Fig. 92, _c_). Inner (caudal) surface with the vastus intermedius.

(2) =M. vastus lateralis= (Fig. 90, _d_).--A flat triangular prismatic mass joined distally to the preceding. It covers the dorsal part of the lateral surface of the thigh.

_Origin_ from a triangular area on the dorsal and lateral surfaces of the shaft and the great trochanter of the femur. The base of the area is at the great trochanter, and its apex is at the junction of the second and third fifths of the shaft on the linea aspera. The linea aspera forms the ventral boundary of the triangle, while its dorsal boundary is formed by a line drawn from its apex to the dorsomedial angle of the great trochanter. The mass unites with the rectus femoris (_c_) by its dorsal border at the junction of the middle and distal thirds of the thigh.

_Insertion_ into the oblique area on the outer surface of the patella near its lateral border in connection with the rectus femoris.

(3) =M. vastus medialis= (Fig. 92, _c_) lies on the medial side of the thigh.

_Origin_ by fleshy fibres over a diamond-shaped area on the shaft of the femur lying between the medial branch of the linea aspera and the area for the vastus lateralis. Proximad the area is bounded by the spiral line, and distad it is bounded by a line parallel to the spiral line and having its proximal end at about the junction of the first and second thirds of the bone. The muscle forms a triangular, prismatic mass. It ends in a thin aponeurosis which is continuous dorsad with the border of the rectus femoris (Fig. 92, _b_), and ventrad sometimes with the tendon of the gracilis (Fig. 91, _b_).

_Insertion_ into the medial border of the patella and the ligamentum patellæ. The insertion may extend onto the head of the tibia.

The adjacent surfaces of the vastus lateralis and the vastus medialis are connected over their distal thirds by an aponeurosis which passes transversely beneath the rectus femoris. The distal end of the aponeurosis is inserted into the proximal border of the patella. Its proximal end receives the insertion of some muscle-fibres which form a part of the vastus medialis as here described. This mass of fibres is described by Strauss-Durckheim as the =crural= muscle. Sometimes the transverse aponeurosis is continuous with only one of the two vasti and sometimes with neither, so that the insertion of the crural of Strauss-Durckheim becomes more or less independent.

_Relations_ of the vastus medialis.--Outer (medial) surface with the sartorius (Fig. 91, _a_) and the structures in the iliopectineal fossa. Cranial (or dorsal) surface with the rectus femoris (Fig. 92, _b_) and vastus intermedius. Caudal (ventral) surface with the pectineus (Fig. 92, _e_), adductor longus (Fig. 92, _f_), adductor femoris (Fig. 92, _g_), and semimembranosus (Fig. 92, _h_).

(4) =M. vastus intermedius.=--A flat mass of muscle which lies beneath the rectus femoris.

_Origin_ from nearly the whole of the dorsal surface of the shaft of the femur between the areas for the vastus medialis and vastus lateralis. The area of origin extends distad to an oblique line the middle of which is about one and one-half centimeters from the patellar surface, the lateral border of the area being longer than the medial border.

_Insertion_ by muscle-fibres into the capsule of the joint. The central fibres are inserted about one centimeter proximad of the patella, while the lateral mass passes to the level of the proximal end.

_Relations._--Outer surface with the rectus femoris (Fig. 92, _b_); borders with the vastus medialis (Fig. 92, _c_) and vastus lateralis (Fig. 90, _d_); inner surface with the femur.

_Action._--The quadriceps extensor is an extensor of the shank. The vastus intermedius acting separately is a tensor of the capsule of the knee-joint.

3. Muscles of the Lower Leg (Crus).

A. ON THE VENTRAL SIDE.--=M. gastrocnemius.=--This is the great muscular mass of the calf. It arises by two heads, the caput laterale or lateral head (Fig. 90, _m_), and the caput mediale or medial head (Fig. 91, _k_), of the gastrocnemius.

=Caput laterale= (Fig. 90, _m_, _m′_, _m″_).--The origin of the lateral head is in four portions:

(1) From the tendon of origin of the plantaris which comes from the middle of the lateral border of the patella. The tendon ends in a small conical mass of fibres (_m′_) which joins the ventral part of the common head.

(2) By a slender flat tendon, distad of the first, from the superficial fascia of the shank (_m″_). The tendon ends in a conical mass which joins the dorsal border of the common head.

(3) By a strong tendon and by muscle-fibres from the distal border of the lateral sesamoid bone (Fig. 61, 3) of the femur. These fibres (_m_) form the middle and outer part of the common head.

(4) By muscle-fibres from the middle of the outer surface of the aponeurosis covering the plantaris (Fig. 90, _l_) along rather more than the proximal half of the tibia. The lateral head thus formed is flat and fusiform in section.

=Caput mediale= (Fig. 91, _k_; Fig. 92, _j_).--The medial head resembles the lateral head closely.

_Origin_ by a strong tendon from the medial sesamoid bone of the femur (Fig. 61, 4) and by muscle-fibres from the surface of the shaft for a short distance proximad of this.

The two heads unite by their contiguous borders at the junction of the first and second thirds of the tibia. The common muscle narrows rapidly and ends in a flat tendon which joins the tendon of the soleus to form the so-called tendon of Achilles (tendo calcaneus) (Fig. 90, _t_). This has its

_Insertion_ into the proximal end of the calcaneus (Fig. 90, 4) near its ventral border. This tendon together with that of the soleus (Fig. 90, _o_) and the fascia of the shank forms a tubular sheath for the tendon of the plantaris.

_Relations._--(1) Of the lateral head. Lateral (outer) surface with the biceps femoris (Fig. 68, _t_) and the superficial fascia. Medial (inner) surface with the popliteus (Fig. 92, _k_), the plantaris (Fig. 90, _l_) (to which it is closely united), the medial head of the gastrocnemius (Fig. 91, _k_), the soleus (Fig. 90, _o_), and the peroneus longus (Fig. 90, _q_). (2) Of the medial head. Medial (outer) surface with the superficial fascia and the tendons of the gracilis (Fig. 91, _b_), semimembranosus (Fig. 92, _h′_), and semitendinosus (Fig. 92, _i_). Lateral (inner) surface at the origin with the adductor femoris (Fig. 92, _g_), then with the plantaris (Fig. 91, _l_), the popliteus (Fig. 92, _k_), flexor longus digitorum (Fig. 91, _n_), and the lateral head of the gastrocnemius (Fig. 90, _m_).

_Action._--Extensor of the foot. (It is to be noted that what is called =extension= in the foot is analogous to what is called =flexion= in the hand, so that the extensors of the foot are most readily to be compared with the flexors of the hand.)

=M. plantaris= (Fig. 90, _l_; Fig. 91, _l_).--A fusiform muscle covered distally by the gastrocnemius, but appearing between the two heads of the gastrocnemius at their proximal ends (Fig. 90, _l_).

_Origin_ by a strong tendon from the middle of the lateral border of the patella and by fleshy fibres from the ventral border of the lateral sesamoid.

The patellar tendon ends in a flattened head which passes ventrad over the lateral epicondyle of the femur and then curves distad; it is closely united with the lateral head of the gastrocnemius. The muscle ends in a thick tendon which passes through a sheath formed by the tendons of the gastrocnemius and soleus, and the fascia of the shank. The tendon passes over the grooved proximal end of the calcaneus onto its ventral surface. It is held in place against the groove by two sheets of aponeurosis, which leave the tendon on either side for a distance of more than a centimeter and are attached to the lateral surfaces of the calcaneus at its proximal end. Lateral motion is thus hindered, while longitudinal motion is permitted.

Between this tendon and the tendon of Achilles is a synovial bursa which aids the gliding movement of the tendon. In the sole of the foot opposite the distal end of the calcaneus the tendon broadens and ends in the flexor brevis digitorum (pedis perforatus) muscle, which might also be considered as a second part of the plantaris. In man the plantaris is inserted into the calcaneus along with the gastrocnemius.

_Relations._--The muscle is covered throughout by the two heads of the gastrocnemius (Fig. 90, _m_; Fig. 91, _k_), except at the proximal end (Fig. 90, _l_), where it is in contact with the integument. Inner surface in relation with the popliteus (Fig. 92, _k_), the soleus (Fig. 90, _o_), the flexor longus digitorum (Fig. 91, _n_), and flexor longus hallucis (Fig. 91, _m_).

=M. soleus= (Fig. 90, _o_).--A flat fusiform muscle lying beneath the plantaris.

_Origin_ by muscle-fibres from the lateral surface of the head of the fibula, and by tendon-fibres from the proximal two-fifths of its ventral border.

_Insertion._--The muscle ends in a slender tendon which joins the lateral border of the gastrocnemius tendon to form the tendon of Achilles (Fig. 90, _t_), which forms the sheath of the plantaris tendon.

_Relations._--Outer surface with the gastrocnemius (Fig. 90, _m_) and plantaris (Fig. 90, _l_). Inner surface with the peroneus longus (Fig. 90, _q_), peroneus tertius (Fig. 90, _r_), and flexor hallucis (Fig. 91, _m_).

_Action._--Assists the gastrocnemius to extend the foot.

=M. triceps suræ.=--The gastrocnemius and the soleus are sometimes considered as forming a single muscle, with three heads, under the name triceps suræ.

=M. popliteus= (Fig. 92, _k_).--A triangular muscle passing from the femur obliquely toward the medial side over the ventral surface of the proximal end of the tibia.

_Origin_ by a strong tendon from the popliteal groove on the surface of the lateral epicondyle of the femur. In the tendon is a sesamoid bone, the popliteal bone (Fig. 61, 5, page 89), which glides over the ventral part of the lateral articular facet on the proximal end of the tibia. As the muscle passes over the joint it is closely attached to the joint capsule. From the popliteal bone, which with the tendon lies within the capsule of the knee-joint, the muscle-fibres diverge to their

_Insertion_ into the proximal end of the ventral surface of the tibial shaft on the medial side of the medial oblique ridge. The area of insertion extends slightly onto the medial surface of the bone.

_Relations._--Outer surface with the gastrocnemius (Fig. 92, _j_) and plantaris (Fig. 91, _l_), and with the tendon of the semitendinosus (Fig. 92, _i_). Distal border with the origins of the soleus and flexor longus digitorum. Inner surface with the capsule of the knee-joint and the tibia.

_Action._--Rotates the thigh so as to turn the toes inward.

* * * * *

The three following deep muscles on the ventral surface of the shank are covered by a deep fascia (the deep crural fascia) which separates them from the overlying muscles. This fascia stretches from the dorsal border of the tibia about the ventral side of the shank to the medial border of the tibia. It sends a slip beneath the border of the fibula.

=M. flexor longus digitorum= (Fig. 91, _m_ and _n_).--Owing to the reduction of the first digit in the cat the tendon of the flexor longus hallucis (_m_) has become united to that of the flexor longus digitorum (_n_), so that the two might be considered separate heads of a single muscle. The head corresponding to the flexor longus hallucis (_m_) is much larger than that corresponding to the flexor longus digitorum (_n_). The two heads will be described separately.

(1) =M. flexor longus hallucis= (Fig. 91, _m_).--This lies against the ventral surface of the tibia and fibula beneath the popliteus (Fig. 92, _k_) and soleus (Fig. 90, _o_).

_Origin_ by fleshy fibres, (1) from the sheet of deep crural fascia which dips between it and the tibialis posterior (Fig. 91, _o_) and the flexor longus digitorum (_n_). (2) From the ventral surface of the tibia distad of the lateral oblique line to within one to three centimeters of the distal end of the shaft. (3) From the medial surface of the shaft and head of the fibula and from the whole interosseous ligament. On the fibular side the origin may extend onto the tendon of the popliteus and the fascia of the peroneus longus. The fibres form a flat fusiform mass ending one centimeter from the heel in a strong flat tendon (_m′_) which passes over the groove on the distal surface of the astragalus and over the groove on the sustentaculum tali. The two grooves are converted into a continuous canal by strong transverse ligaments, and the canal is lined by an extension of the synovial bursa of the ankle-joint. Emerging from the canal the tendon broadens and receives on its medial side the insertion of the tendon of the flexor longus digitorum (_n_). The tendon gives origin on its outer surface to the lumbricales and to the common plantar ligament. The tendon continues to broaden until it reaches the middle of the length of the metacarpals; here it divides into four tendons which pass to the terminal phalanges of the digits.

_Insertion._--The relations of the four tendons and their insertions are identical with those of the flexor profundus digitorum of the hand.

_Relations._--Outer surface with the soleus (Fig. 90, _o_) and plantaris (Fig. 91, _l_). Lateral border with the soleus, the peroneus tertius (Fig. 90, _r_), and peroneus brevis (Fig. 90, _s_). Medial border with the tibialis posterior (Fig. 91, _o_) and flexor longus digitorum (Fig. 91, _n_).

_Action._--Flexor of the phalanges.

(2) =M. flexor longus digitorum= (Fig. 91, _n_).

_Origin_ by muscle- and tendon-fibres from the ventral surface of the tibia over its proximal half between the oblique ridges; by fleshy fibres from an aponeurosis between it and the tibialis posterior (Fig. 91, _o_), and by tendon from the medial surface of the head of the fibula. At the junction of the middle and distal thirds of the bone the muscle ends in a slender tendon which passes through the ventral groove on the medial surface of the tibia and, curving onto the sole of the foot, becomes attached to the medial border of the common tendon described under the last.