Part 48

Action.--Assists the iliopsoas.

B. MUSCLES ON THE MEDIAL SURFACE OF THE HIP.--=M. obturator internus= (Fig. 90, e).--The obturator internus appears as a triangular muscle caudad of the gemellus superior.

Origin by numerous small separate heads from the dorsal surface of the ramus of the ischium along its symphysis and following its medial border from the symphysis nearly to the tuberosity. The fibres form a flat muscle which narrows and passes through the lesser sciatic notch, turns ventrad and ends in a strong flat tendon whose

Insertion is into the bottom of the trochanteric fossa of the femur. The tendon is continued proximad on the inner surface of the muscle and forms a smooth firm surface by which the muscle glides over the dorsal border of the ischium. Into the inner surface of this tendon near its insertion the tendon of the gemellus inferior is inserted.

Relations.--Medial surface within the pelvis with a mass of fat separating it from the pelvic organs. Dorsal or outer surface with the biceps femoris, the tenuissimus, the caudofemoralis, and the great sciatic nerve. Inner surface with the ischium and the great sciatic nerve. Caudal (or ventral) border with the quadratus femoris.

Action.--Abductor of the thigh.

=M. iliopsoas= (Fig. 162, 8; Fig. 91, c).--The iliopsoas (equivalent to the human psoas and iliacus) is a conical muscle emerging from the abdominal cavity onto the medial surface of the femur.

Origin.--(a) The portion corresponding to the human psoas (Fig. 162, 8) arises by ten vertebral heads. The first five of these come from the five cranial tendons of origin of the psoas minor (Fig. 162, 9); the sixth from a tendinous expansion which passes from the tendon of the first head over the ventral longitudinal muscles to the transverse process of the fifth lumbar vertebra. The seventh, eighth, ninth, and tenth heads arise by fleshy fibres from the ventral surfaces of the centra of the last four lumbar vertebræ.

(b) The portion corresponding to the human iliacus arises by fleshy fibres from the ventral border of the ilium, from opposite the auricular impression to the iliopectineal eminence. The portions of the muscle all converge to form a conical mass which ends in a strong tendon lying on its outer surface.

Insertion by tendon and fleshy fibres into the apex of the lesser trochanter of the femur.

Relations.--Dorsal surface with the quadratus lumborum (with which this muscle is partly united), the rectus femoris (Fig. 91, d), and, by the iliac head, with the gluteus minimus. Ventral and medial surface with the psoas minor (Fig. 162, 9) and the peritoneum. Lateral edge with the transversus abdominis (Fig. 162, 4).

Action.--Rotates the thigh so as to carry the foot out; also flexes the thigh.

2. Muscles of the Thigh.

=M. biceps femoris= (Fig. 68, t, page 117).--A very large flat muscle covering about two-thirds of the lateral side of the thigh.

Origin (Fig. 90, 2).--From the ventral surface of the tuberosity of the ischium by tendon- and muscle-fibres. The fibres diverge, and near the knee the mass has spread out, ending in a fascia. The dorsal border of the muscle and the common fascia are continuous dorsad with the superficial fascia of the thigh and with the tendon of the caudofemoralis (Fig. 68, s). Ventrad it is continuous with the superficial fascia of the shank.

Insertion into rather more than the proximal one-third of the dorsal border of the tibia along its lateral margin and into the lateral margin of the patella. In passing over the knee-joint it is closely united to the underlying ligaments and tendons.

Relations.--Outer surface with the superficial fascia and with a few of the most caudal fibres of the cutaneus maximus (Fig. 62, b, page 94). Cranial (or dorsal) edge with the caudofemoralis (Fig. 68, s) and the vastus lateralis (Fig. 90, d). Caudal border with the semitendinosus (Fig. 68, u) and a mass of fat. Inner surface with the caudofemoralis (Fig. 68, s), the tenuissimus (Fig. 90, g), the obturator internus (Fig. 90, e), the quadratus femoris (Fig. 90, f), the semitendinosus (Fig. 68, u), the semimembranosus (Fig. 90, i), the adductor femoris (Fig. 90, h), the great sciatic nerve (Fig. 163, a), and distad with the following muscles of the lower leg: the tibialis anterior (Fig. 90, n), the extensor longus digitorum (Fig. 90, p), the peroneus longus (Fig. 90, q), and the lateral head of the gastrocnemius (Fig. 90, m).

Action.--Abductor of the thigh, and flexor of the shank.

=M. tenuissimus= or =M. abductor cruris= (Fig. 90, g).--A very slender muscle, only three or four millimeters wide.

Origin from the tip of the transverse process of the second caudal vertebra, in common with the caudofemoralis (Fig. 68, s) or gluteus maximus. It passes obliquely beneath the biceps femoris (Fig. 68, t) distad and ventrad, to the distal end of the ventral border of that muscle. Here it becomes continuous with the ventral border of the biceps, ending in a continuation of the same fascia into which the biceps is inserted.

Relations.--Outer surface with the caudofemoralis (Fig. 68, s) and the biceps femoris (Fig. 68, t); distad with the integument. Inner surface with the obturator internus (Fig. 90, e), quadratus femoris (f), semitendinosus (j), adductor femoris (h), semimembranosus (i), and distad with the muscles of the lower leg.

=M. caudofemoralis= (=parameralis=, Strauss-Durckheim) (Fig. 68, s, page 117).

Origin by a flat tendon from the transverse processes of the second and third caudal vertebræ. The muscle forms a flat band which passes distad along the middle of the lateral side of the thigh over the pelvis and caudad of the great trochanter. At the middle of the thigh it ends in a very thin tendon. The tendon passes distad along the medial surface of the biceps femoris (Fig. 68, t), pierces the fascia lata near the knee, and passes to its

Insertion into the middle of the lateral border of the patella.

Relations.--Outer surface with the superficial fascia and a few fibres of the cutaneus maximus; distad with the biceps femoris (Fig. 68, t). Cranial border with the gluteus maximus; caudal border with the biceps femoris. Inner surface with the tenuissimus (Fig. 90, g), the gluteus maximus, the abductor caudæ internus, and with the obturator internus (Fig. 90, e); distad with the vastus lateralis.

Action.--Abducts the thigh and helps to extend the shank.

=M. semitendinosus= (Fig. 90, j).--A long slender muscle on the ventral (caudal) border of the thigh, between the semimembranosus (i) and the biceps femoris (Fig. 68, t).

Origin from the apex of the tuberosity of the ischium beneath the origin of the biceps femoris. The muscle passes to the medial side of the shank and ends in a thin but strong tendon (Fig. 92, i′) about five millimeters broad. The tendon curves proximad and passes beneath the gracilis tendon (Fig. 91, b) to its