Part 46

Origin by a flat tendon from the ventral surface of the os magnum on the ulnar side of the adductor pollicis (b). It passes toward the ulnar side and distad, the fibres diverging to their

Insertion (1) into nearly the whole of the radial surface of the fifth metacarpal, (2) into the base of its first phalanx.

V. MUSCLES OF THE PELVIC LIMBS.

=1. Muscles of the Hip.=

A. ON THE LATERAL SURFACE OF THE HIP.

=Fascia of the Thigh.=--After the removal of the superficial fascia with its fat and blood-vessels, there is seen a strong glistening fascia, the =fascia lata= (Fig. 68, z, page 117), covering the vastus lateralis muscle over the dorsal half of the thigh. Ventrally it dips between the vastus lateralis and the biceps femoris and, becoming gradually thinner, is lost on the surface of the former muscle. Passing over the dorsal border of the thigh, it extends beneath the sartorius and is attached to the dorsal border of the vastus medialis. Toward its distal end the fascia is continuous with the tendon of the biceps femoris and dorsad with the border of the sartorius muscle, while between these points it is united with the tendon of the vastus lateralis; it thus gains insertion into the patella. At its proximal end the fascia receives the insertion of the tensor fasciæ latæ (Fig. 68, r).

=M. tensor fasciæ latæ= (Fig. 68, r, page 117; Fig. 92, a).--The tensor fasciæ latæ is a thick triangular muscle which may be recognized by its insertion into the proximal end of the fascia lata (Fig. 68, z; Fig. 92, a′).

Origin by fleshy fibres as a thick triangular prism from the outer margin of the ventral border of the ilium craniad of the auricular impression and from the fascia covering the ventral border of the gluteus medius (Fig. 90, b) over its cranial half. The caudal border of the muscle may be continuous with the cranial border of the gluteus maximus. The muscle spreads out in a fan-like manner, covering the proximal third of the dorsal surface of the thigh. The cranial fibres pass farther distad than the others.

Insertion into the fascia lata (Fig. 68, z) along an irregular line which begins caudad at the base of the great trochanter and ends on the cranial side of the thigh at the junction of the first and second thirds.

Relations.--Outer surface with the cutaneus maximus (Fig. 62, b, page 94) and craniad with the sartorius (Fig. 68, q). Cranial border with the sartorius (q); caudodorsal border with the gluteus medius (Fig. 90, b). Inner surface with the gluteus medius, the rectus femoris (Fig. 92, b), and the vastus lateralis (Fig. 90, d).

Action indicated by the name. It also assists the quadriceps femoris in extending the leg.

=M. gluteus maximus.=--The gluteus maximus is a rather small quadrangular muscle in the angle between the gluteus medius (Fig. 90, b) and the caudal vertebræ.

Origin (Fig. 163, 3, page 401) by fleshy fibres from the tips of the transverse processes of the last sacral and the first caudal vertebræ, from the fascia covering the spinous muscles dorsad of the transverse processes of these vertebræ, and from the fascia covering the gluteus medius. The muscle passes laterad and slightly caudad to its

Insertion by tendon and muscle-fibres into a tubercle on the caudal side of the great trochanter at the middle of its distal end, and for a few millimeters into the ridge which continues distad from this tubercle.

Relations.--Outer surface with the caudofemoralis (Fig. 68, s, page 117), the superficial fascia, and a few fibres of the cutaneus maximus. Inner surface with the abductor caudæ internus, the tenuissimus (Fig. 90, g), the great sciatic nerve (Fig. 163, a), the obturator internus (Fig. 90, e), the gluteus medius (Fig. 90, b), the gemellus superior, and the pyriformis (Fig. 163, 7). Cranial border with the gluteus medius and the tensor fasciæ latæ. Caudal border with the caudofemoralis (Fig. 68, s).

Action.--Abducts the thigh.

=M. gluteus medius= (Fig. 90, b).--The gluteus medius is a very large triangular muscle which connects the ilium and the sacrum with the great trochanter (1).

Origin by fleshy fibres (1) from the superficial sacral fascia; (2) from the lateral surface of the fascia which covers the surface of the supraspinous extensor muscles of the tail; (3) from the fascia intervening between it and the tensor fasciæ latæ; (4) by tendon fibres from the dorsal half of the crest of the ilium and its dorsal border, and the dorsal half of the lateral surface craniad of the auricular impression; and (5) from the tips of the transverse processes of the last sacral and the first caudal vertebræ. The fibres converge to a strong internal tendon.

Insertion into the proximal end of the great trochanter.

Relations.--Outer surface with the gluteus maximus and tensor fasciæ latæ, and between these with the strong fascia lying beneath the cutaneus maximus muscle. Inner surface with the gluteus minimus, the pyriformis, and the gemellus superior. Cranial border with the tensor fasciæ latæ. Caudal border with the gluteus maximus.

Action.--Abducts the thigh.

=M. pyriformis= (Fig. 163, 7).--The pyriformis is a triangular muscle covered by the gluteus maximus and the gluteus medius (Fig. 90, b) and overlying the gemellus superior (Fig. 163, 6).

Origin by fleshy fibres from the tips of the transverse processes of the last two sacral and the first caudal vertebræ. The muscle passes laterad through the great sciatic notch to its

Insertion by a flat tendon into an elongated area on the proximal border of the great trochanter just outside (caudad) of the insertion of the gemellus superior.

Relations.--Outer surface with the gluteus medius (Fig. 90, b) and the gluteus maximus. Inner surface with the gemellus superior (Fig. 163, 6), the great sciatic nerve (Fig. 163, a), and the flexor caudæ longus (Fig. 68, x).

Action.--Abductor of the thigh.

=M. gemellus superior= (Fig. 163, 6).--The gemellus superior is a triangular muscle lying beneath the pyriformis (Fig. 163, 7). It is broader than the pyriformis, so that it projects beyond its borders both caudad and craniad. It is closely united craniad with the gluteus minimus, so that the limits of the two are definable only with difficulty. Its caudal border is closely united to the gemellus inferior.

Origin by fleshy fibres from an elongated area on the dorsal border of the ilium and ischium. The area is narrowed craniad. It does not quite reach the posterior inferior iliac spine in the one direction nor the spine of the ischium in the other direction. The fibres converge to a strong tendon the