Part 49

Insertion into the crest (dorsal border) of the tibia one or two centimeters from its proximal end.

Relations.--Lateral surface with the biceps femoris (Fig. 68, t), the integument, a mass of fat, and distad with the gastrocnemius (Fig. 92, j) and popliteus (Fig. 92, k). Caudal surface with the integument. Medial surface with the semimembranosus (Fig. 90, i) and distad with the integument of the lower leg.

Action.--Flexor of the shank.

=M. semimembranosus= (Figs. 90 and 91, i; Fig. 92, h).--A thick prismatic muscle lying along the ventral (or caudal) side of the thigh between the semitendinosus (j) and the gracilis (Fig. 91, b).

Origin by short tendon-fibres from the caudal border of the tuberosity and the ramus of the ischium. The muscle mass is divided throughout most of its length into two portions (Fig. 92, h and h′), one of which (h′) lies laterad and caudad of the other. The two portions pass to the medial side of the knee. The caudal portion (h′) ends in a strong flat tendon five millimeters broad, the

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.

a, M. sartorius; b, M. gracilis; c, M. iliopsoas; d, M. rectus femoris; e, M. vastus medialis; f, M. pectineus; g, M. adductor longus; h, M. adductor femoris; i, M. semimembranosus; j, M. semitendinosus; k, medial head of M. gastrocnemius; l, M. plantaris; m, M. flexor longus hallucis (m′, its tendon); n, M. flexor longus digitorum; (n′, its tendon); o, M. tibialis posterior; p, M. tibialis anterior; q, M. interosseus of second digit. 1, patella; 2, calcaneus; 3, medial malleolus; 4, second metatarsal; 5, transverse ligament of the lower leg.]

=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.