Part 18

_Origin_ by fleshy fibres from the ventral border of the os magnum. It curves about the base of the first metacarpal on its ulnar side to its insertion.

_Insertion_ by fleshy fibres into the base of the first phalanx of the pollex on its ulnar side.

C. MUSCLES LYING BETWEEN THE METACARPALS.--=Mm. interossei= (Fig. 89).--Small stout muscles lying on the palmar surfaces of the metacarpals of the second, third, fourth, and fifth digits.

_Origin_ by fleshy fibres from the ventral or lateral surfaces of the bases of the metacarpals. Near the distal end of the metacarpal each divides into two masses which pass onto the lateral surfaces of the metacarpal, so as to leave the ventral surface of the distal end exposed.

_Insertion_ partly onto the lateral surfaces of the base of the first phalanx and its sesamoids, and partly by a slender tendon (Fig. 84, _h_) which is continued dorsad to join the extensor tendon of the digit.

D. SPECIAL MUSCLES OF THE SECOND DIGIT (THE INDEX).--=M. flexor brevis digiti secundi= (or indicis).--This name may be applied to M. interosseus of the second digit (Fig. 89, _c_).

=M. abductor digiti secundi.=--This name might be applied to a portion of the interosseus of the second digit which is sometimes differentiated from the remainder.

_Origin_ from the radial and ventral surfaces of the base of the second metacarpal, and from the ventral surface of the trapezium.

_Insertion_ into the radial side of the base of the first phalanx of the second digit and into its sesamoid.

=M. adductor digiti secundi= (Fig. 89, _d_).

_Origin_ from the ventral surface of the os magnum.

_Insertion_ into the ulnar side of the base of the first phalanx of the second digit.

E. SPECIAL MUSCLES OF THE FIFTH DIGIT.--=M. abductor digiti quinti= (Fig. 89, _i_).--A thick, small, conical bundle.

_Origin_ from the distal surface of the pisiform bone and from the transverse ligament on the ulnar side of the pisiform. It ends in a slender tendon which runs along the ulnar side of the fifth metacarpal to its

_Insertion_ into the ulnar side of the base of the first phalanx of the fifth digit.

=M. flexor brevis digiti quinti= (Fig. 89, _h_; Fig. 88, _e_).--This covers the ventral surface of the fifth metacarpal, and is really the interosseus of this digit.

_Origin_ by fleshy fibres from the ventral surface of the base of the fifth metacarpal; from the ventral process of the unciform bone, and from the transverse ligament proximad of the fifth metacarpal.

_Insertion_ by fleshy fibres into the ventral border of the proximal end of the first phalanx of the fifth digit.

=M. opponens (adductor) digiti quinti= (Fig. 89, _g_).

_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

_Insertion_ of which is into a triangular area dorsad of the tip of the great trochanter.

_Relations._--Outer surface with the gluteus medius (Fig. 90, _b_), the pyriformis (Fig. 163, 7), the great sciatic nerve (Fig. 163, _a_), and the gluteus maximus. Inner surface with the ilium, ischium, the capsularis, the caudal edge of the gluteus minimus (Fig. 163, 5), and the cranial edge of the obturator internus (Fig. 90, _e_).

_Action._--Rotates the femur and abducts it so as to carry the foot outward.

=M. gluteus minimus= (Fig. 163, 5).--The gluteus minimus is a long triangular muscle beneath the middle of the gluteus medius (Fig. 90, _b_) and with its caudal border against or covering the cranial border of the gemellus superior (Fig. 163, 6), to which it is frequently closely united.

_Origin_ from the ventral half of the ilium, from near its cranial end to a point midway between the posterior iliac spine and the spine of the ischium. The muscle ends in a strong flat tendon.

_Insertion_ into an oval facet at the base of the dorsal surface of the great trochanter on its lateral side.

_Relations._--Outer surface with the gluteus medius (Fig. 90, _b_) and at the caudal border with the gemellus superior (Fig. 163, 6). Inner surface with the capsularis and rectus femoris (Fig. 92, _b_).

_Action._--Rotates the femur so as to carry the foot out.

=M. capsularis= (gluteus quartus, or epimeralis).--The capsularis is a small flat bundle of muscle-fibres which lies obliquely beneath the gluteus minimus (Fig. 163, 5) and gemellus superior (6) on the lateral or outer surface of the ilium.

_Origin_ by fleshy fibres from the surface of the ilium over a triangular area between the origin of the rectus femoris (Fig. 92, _b_) ventrad, the gemellus superior (Fig. 163, 6) dorsad, and of the gluteus minimus (Fig. 163, 5) craniad and the acetabulum caudad. The muscle passes over the smooth surface of the ilium and the pubis ventrad of the acetabulum and then over the capsule of the joint.

_Insertion_ by fleshy fibres for about one centimeter in the middle line on the dorsal surface of the femur distad of the great trochanter.

_Relations._--Outer surface with the gluteus minimus (Fig. 163, 5), the gemellus superior (6), and the vastus lateralis (Fig. 90, _d_). Inner surface with the ilium, the rectus femoris (Fig. 92, _b_), the capsule of the joint, and the vastus medialis (Fig. 92, _c_).

_Action._--Rotates the thigh so as to carry the foot inward, hence antagonizes the iliopsoas.

=M. gemellus inferior.=--The gemellus inferior is a flat triangular muscle situated just caudad of the gemellus superior and beneath the obturator internus (Fig. 90, _e_), so that it is seen on reflecting the latter

_Origin_ from the dorsal one-half of the whole lateral surface of the ischium between the ischial spine and the ischial tuberosity. The fibres converge toward its insertion. The inner surface of the muscle is covered by a strong tendon.

_Insertion_ into the inner surface of the tendon of the obturator internus (Fig. 90, _e_) by tendon- and muscle-fibres. Some of the muscle-fibres are inserted into the capsule of the joint.

_Relations._--Outer surface with the obturator internus (Fig. 90, _e_). Medial surface with the ischium. Caudal border with the quadratus femoris (Fig. 90, _f_). Cranial border with the gemellus superior.

_Action._--Abductor of the thigh. The muscle may be considered as a separate head of the obturator internus (Fig. 90, _e_).

=M. quadratus femoris= (Fig. 90, _f_).--The quadratus femoris is a short thick muscle connecting the ischial tuberosity (2) and the proximal end of the femur. It lies just caudad of the obturator internus (_e_) beneath the proximal end of the biceps femoris (Fig. 68, _t_).

The _origin_ is by fleshy fibres from a considerable triangular area on the lateral surface of the ischium near the tuberosity. The area lies between the origin areas of the gemellus inferior, biceps, semimembranosus, and the obturator externus.

_Insertion_ into the distal two-thirds of the ventral border of the great trochanter and about half the adjacent surface of the lesser trochanter.

_Relations._--Outer surface with the tenuissimus (Fig. 90, _g_), the biceps (Fig. 68, _t_), the semitendinosus (Fig. 90, _j_), and the great sciatic nerve (Fig. 163, _a_). Caudal border with the semimembranosus (Fig. 90, _i_). Ventral border with the adductor femoris (Fig. 90, _h_); dorsal border with the obturator internus (Fig. 90, _e_) and gemellus inferior.

_Action._--Extensor of the thigh and rotator of the femur so as to carry the foot inward.

=M. obturator externus.=--The obturator externus is a flat triangular muscle beneath the adductor femoris (Fig. 92, _g_).

_Origin_ by fleshy fibres from the median lip of the obturator foramen and from both dorsal and ventral surfaces of the rami of the pubis and ischium adjacent to the lip. Also from the outer surface of the ramus of the ischium as far as the area for the quadratus femoris (Fig. 90, _f_). The fibres converge to a strong flat tendon.

_Insertion_ into the proximal portion of the bottom of the trochanteric fossa.

_Relations._--Ventral surface with the adductor femoris (Fig. 92, _g_). Dorsal surface with the pubis and ischium. Caudal border with the quadratus femoris (Fig. 90, _f_).

_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

_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