This muscle lies most internally, and corresponds to the m. flexor digitorum sublimis of man. It arises in common with the foregoing muscle from the epicondylus medialis, and runs downwards to the palm of the hand. At its entrance into this it diminishes and passes into the flat aponeurosis palmaris. (See hand, B.)

60. M. flexor antibrachii medialis (Ecker), (Fig. 75 Fa).

63. M. extensor digitorum communis longus (Fig. 75 ed).

67. M. flexor digitorum communis and m. palmaris brevis (Fig. 77 fd, pb).

The origin and course of this muscle has been described above. At its entrance into the palm it suddenly diminishes in size and passes into a triangular aponeurosis, aponeurosis palmaris. Into the outer border of this aponeurosis is inserted the m. palmaris brevis (Fig. 77 pb); this latter muscle arises from the posterior or ulnar border of the lower extremity of the radio-ulnar below the insertion of the mm. anconaei, and runs obliquely downwards to this insertion.

From the lower free border of the aponeurosis a number of muscles arise which will be described with the rest of the digital muscles.

(2) Muscles of the rudimentary thumb.

68. M. abductor pollicis (Figs. 77, 78 ap).

This short muscle arises from the upper border of the lower extremity of the radio-ulnar, passes transversely outwards, and is then inserted into the anterior border of the rudimentary thumb.

69. M. adductor pollicis (Figs. 77, 78 ad.p).

This lies more superficially than the last, it arises from the palmar surface of the os capitato-hamatum, and is inserted together with the abductor pollicis into the thumb. Several fibres of the extens. dig. II brevis are also inserted into the thumb. As this member is completely covered with skin, the motions of which it is capable are very limited.

(3) Muscles of the second finger, which serves the purposes of a thumb.

70. M. flexor digiti II longus s. sublimis (Fig. 77 f2).

This is a flat muscle, which arises for the most part by fleshy fibres from the hinder free border of the aponeurosis palmaris, also by a smaller part from the palmar surface of the os capitato-hamatum. It quickly passes into a thin long tendon which is inserted into the terminal phalanx of the thumb (second finger).

71. M. flexor digiti II brevis s. profundus (Fig. 77 fb2).

This flat muscle, covered by the preceding, has a tendinous origin from the palmar surface of the os capitato-hamatum, together with one head of the flexor sublimis, and is inserted into the basal phalanx.

72. M. flexor digiti II tertius (Fig. 78 fb2′).

73. M. adductor digiti II (Fig. 78 ad2).

84. M. flexor dig. V longus s. sublimis (Fig. 77 f5).

This corresponds exactly with the corresponding muscle of the fourth finger.

85. M. flexor dig. V brevis (Fig. 77 fb5).

This muscle arises from the free border of the aponeurosis and is inserted into the basal phalanx.

86. M. flexor proprius phalangum dig. V (Fig. 78 fp).

It corresponds exactly with the corresponding muscle of the fourth finger.

87. M. opponens dig. V (Fig. 78 o′).

This muscle has a narrow origin from the palmar surface of the os capitato-hamatum, it widens and is inserted into the outer border of the metacarpal of the small finger. It draws this finger towards the thumb.

88. M. abductor dig. V primus (Figs. 77 and 78 ab5).

This muscle arises from the palmar border and the outer surface of the os pyramidale, and is inserted into the basal phalanx by a thin tendon.

89. M. abductor dig. V secundus (Figs. 77 and 78 ab5′).

It arises from the posterior part of the os pyramidale, is short, and is inserted into the outer side of the metacarpal.

(II.) Muscles on the dorsal surface.

M. extensor digitorum communis longus (Figs. 75 ed and 77 ec).

90. M. extensor digitorum communis brevis (Fig. 79 e3, e4, e5).

Covered by the foregoing, this muscle arises from the os pyramidale in conjunction with the extensor pollicis and from the os capitato-hamatum. The part destined for the third finger, together with that for the fourth, arises from the os pyramidale, passes obliquely backwards into a tendon which runs along the inner side of the corresponding finger to be inserted into the last phalanx. That for the fifth finger arises from the inner projection of os capitato-hamatum being here attached to the insertion of the m. extensor carpi ulnaris, and is inserted in a similar manner into the terminal phalanx of the fifth finger.

91. M. abductor digiti II (i.e. pollicis) longus (Figs. 74 ei and 79 ab.2).

For the origin and course of this muscle in the forearm see No. 63. The muscle passes obliquely over the wrist-joint from the little finger towards the inner side and from before backwards, it is inserted into the metacarpal of the second finger (thumb). The place of insertion of this muscle into the metacarpal (compare p. 47) is, in the males, developed into a ridge and process, the muscle itself is enlarged during the breeding season. This muscle abducts the thumb and by this means presses upon the chest of the female when clinging to her.

92. M. extensor digiti II proprius longus (Fig. 79 e2, e2′).

This muscle lies obliquely on the back of the hand, parallel with the m. abductor digiti II. It arises by two heads, one from the tendon of the flexor antibr. lat. superf. (n. 60) upon the hinder extremity of the radio-ulnar. This tendon conceals the hinder end of this bone by means of a patella-like thickening, and sends forth three tendinous prolongations; of these, the one is attached to the ulnar border of the radio-ulnar, the second to the os naviculare, while the third constitutes that portion of the m. extens. dig. II proprius long. which is under consideration. The second head arises from the os pyramidale in connection with the extensor digitorum communis brevis (n. 90). The heads unite to form a long muscle, which runs obliquely towards the second finger, passes into a tendon, which, after forming connections by some muscular fibres with the metacarpal, is inserted into the terminal phalanx.

93. M. extensor dig. II proprius brevis (Fig. 79 eb2).

This muscle lies between the preceding muscle and the abductor dig. II longus. It arises from the os naviculare, and also includes some fibres which arise from the second metacarpal. The tendon runs along the radial side and is inserted along with the last muscle into the terminal phalanx.

94. M. abductor dig. II brevis (Fig. 79 ab.2′).

This represents the abduct. pollic. brevis of man, lies on the outer side of the hand, arises from the os naviculare, and is inserted into the second metacarpal.

95. M. extensor dig. III proprius.

This muscle has two heads of origin, from the os naviculare and lunatum. These form one muscular belly, which rapidly diminishes and passes into a tendon; this, after receiving a few muscular fibres from the second metacarpal, runs to the outer part of the dorsal surface of this finger as far as the terminal phalanx, where it is inserted.

96. M. extensor dig. IV proprius.

By a somewhat broad base, this muscle arises from the os naviculare and lunatum. The tendon receives fibres from the fourth metacarpal and runs on the outer half of the dorsal surface of this finger as far as the middle phalanx, where it is inserted.

(III.) MM. interossei.

97, 98. [a.] MM. transversi metacarpi (Ecker), (Fig. 78 t, t′, ad2).

These lie transversely between the metacarpals. There are three; the first has been already described as m. adductor digiti II (n. 73); the second is stretched between the third and fourth metacarpals, and the third between those of the fourth and fifth fingers.

99, 100, 101. [b.] MM. interossei volares.

One may regard as such, four long, thin muscles, which take origin near one another on the palmar surface of the carpal bones, and diverge from this towards the second and fifth fingers.

1. The first of these muscles (Fig. 78 fb2′) has already been described above as the m. flexor digiti II tertius (n. 72).

2. The second (Fig. 78 i3) passes from the origin already described to the palmar surface of the basal phalanx of the third finger.

3. The third (Fig. 78 i4) runs, in like manner, to the fourth finger.

4. The fifth (Fig. 78 i5) to the fifth finger‍46.

102 to 108. MM. interossei dorsales.

These arise in common from the metacarpals, and are inserted into the basal phalanx of the corresponding surface on the finger.

1. The third finger has two, one to the radial side (Fig. 79 i′3), one to the ulnar side.

2. The fourth finger has three, the third (Fig. 79 i′4) arises from the carpus, and perhaps ought rather to be regarded as an extensor.

3. The fifth finger has two.

IV. MUSCLES OF THE HINDER LIMB.

I. Muscles of the Thigh.

General arrangement (Figs. 80, 81).

a. The m. triceps femoris forms the outer border of the thigh, and extends on to both the dorsal and ventral surfaces. The outer border therefore corresponds with the anterior surface of the thigh of man, in consequence of the thigh in the frog being normally rotated outwards.

b. The m. vastus internus (v.i.) and a portion of the adductor longus (ad′), the sartorius (s), a portion of the adductor magnus (ad‴), and the rectus internus major (r.i′) are found on the inner surface of the thigh.

c. The rectus internus minor (r.i″) forms the inner border.

d. On the dorsal surface are to be seen, nearest the trunk, the glutaeus (gl), on the outer border the vastus externus (v.e.), the pyriformis and biceps (p and b), then the semimembranosus (sm), and lastly the rectus internus minor (ri″).

e. By reflecting the rectus internus major (compare Fig. 82) there are exposed to view: the semitendinosus (st), the whole length of the adductor longus, magnus (ad′ and ad‴), and brevis (ad″). By reflecting the triceps, one sees (Figs. 84, 85) the ilio psoas (ip), and beneath the semimembranosus, the quadratus (qf), and capsularis femoris (og).

Description of the separate Muscles.

(A.) Muscles of the dorsal surface.

109. M. glutaeus (Fig. 80 gl).

Dugès, ex-ilio-trochantérien.—Zenker, glutaeus maior.

The tendinous origin of this muscle is found on the outer surface and upper border of the two hinder thirds of the iliac bone. Thence it runs outwards and backwards between the head of the m. vastus externus (ve) on the one side, and the ilio-psoas and rectus anticus (ra) on the other, to be inserted into a tubercle (trochanter) of the femur.

110. M. Pyriformis (Fig. 80 p).

A narrow, slender muscle, arising from the apex of the coccyx; it passes obliquely outwards and backwards to the thigh, to be inserted deeply between the m. vastus externus and the biceps, into the inner surface of the femur, but towards the ventral surface.

M. triceps femoris s. extensor cruris communis (Fig. 80).

This is a large, strong muscle, having three heads of origin, and inserted by a tendon into the tibio fibula. The three heads are the caput longum or the rectus femoris anticus (r.a.), the caput externum or the vastus externus (v.e.), and the caput internum or the vastus internus (Fig. 82 vi); of these, the first is situated on the outer border of the thigh, the second on the dorsal surface, and the third on the ventral surface.

111. [a.] M. rectus femoris anticus (Figs. 80, 82 ra).

This arises from the under (ventral) surface of the iliac bone about its middle and beneath the m. glutaeus. The muscular belly quickly passes into an aponeurosis, which covers the other two muscular masses and combines with their tendons.

112. [b.] M. vastus externus (Fig. 80 v.e.).

It arises from the upper and hinder extremity of the iliac bone (Fig. 42 il′) behind the glutaeus, which here sinks in between this muscle and the rectus anterior.

113. [c.] M. vastus internus (Figs. 81, 82 vi).

It arises from the whole of the under and outer surfaces of the hip-joint capsule, and from tendinous slips which pass from this capsule downwards on the under surface of the muscle, (from the pubis and the femur I have not seen any fibres of origin, as stated by others). Anteriorly the vastus may easily be separated into two heads. The two vasti unite and form one muscular belly, in the formation of which, as above stated, the rectus anticus takes no part. This united muscle passes into a tendon which, without the mediation of a patella, passes over the knee-joint to be inserted into the anterior extremity of the tibio fibula, and is prolonged into the fascia of the leg.

114. M. ilio-fibularis s. biceps (Fig. 80 b).

This is a long, somewhat narrow muscle, which lies to the inner side of, and partly covered by, the vastus externus, between which and the semimembranous it is placed. It arises by a tendon between the ilio-psoas and pyriformis from the ilium above the acetabulum and behind the origin of the vastus externus. From here it passes backwards, separated from the vastus externus by a strong ligam. intermusculare. On the inner side of this muscle, between it and the m. semimembranosus, run the vessels of the thigh and the N. ischiadicus. The muscle then divides into two portions, of which one is inserted high up on the inner and under surface of the femur. This is probably the muscle which Klein (l. c., p. 61) describes as the extensor brevis. The other long muscular belly passes into a thin tendon, opposite the hinder extremity of the thigh, it divides into two portions; the anterior is inserted into the dorsal surface of the hinder extremity of the femur, the other into the dorsal surface of the tibio-fibula. Between the two is stretched an arch with the concavity outwards. This insertion of the biceps is covered by the stronger tendon of origin of the m. gastrocnemius (compare Fig. 87).

115. M. semimembranosus (Figs. 80, 86 sm).

This muscle lies on the dorsal surface of the thigh, to the inner side of the biceps and pyriformis: it is a broad muscle, which takes a tendinous origin from the hinder and upper angle of the symphysis ossis ilei, and is inserted by a flat tendon into the dorsal surface of the ligaments of the knee-joint, and through these into the tibio-fibula. The tendon is formed rather abruptly from the muscle, and is surrounded (Fig. 86) by the concave arch, which forms the tendon of origin of the gastrocnemius (q. v.). A little behind its middle (compare Fig. 81) the muscle is divided obliquely into an anterior and a posterior portion by an aponeurotic septum. As all the fibres are interrupted by this structure, the muscle may very easily be torn through.

(B.) Muscles on the ventral surface.

116. M. sartorius (Figs. 81, 82 s).

This long, flat muscle lies along the middle of the ventral surface of the thigh; it arises by a tendon from the anterior inferior angle formed by the symphysis of the innominate bones, and terminates in a tendon behind the knee-joint, forming a kind of pes anserinus in the fascia of the leg, similar to that of the semitendinosus‍47.

117. M. rectus internus major (Ecker), (Figs. 81 r.i′, 82 ri′).