Part 45

Origin.—The muscular belly may be easily divided into two parts. The inner head extends from the head of the tibia immediately beneath the peroneus longus. The outer head arises by a strong tendon from a depression on the antero-inferior ridge of the outer condyle of the femur.

Insertion.—The tendon passing through the fibrous ligamentous loop just above the tibial condyles, inserts to a tubercle on the shaft just below the head of the tarso-metatarsus.

Shape.—Large, fusiform.

Relations.—Beneath the peroneus longus.

Action.—Flexes the metatarsus upon the tibia.

=Extensor Longus Digitorum= (Fig. 25, No. G, 6). Location.—Anterior tibial region.

Origin.—From the inferior portion of the crest and a portion of the shaft of the fibula.

Insertion.—It becomes tendinous at the lower third of the bone, passing under the bony ridge just above the condyle in front, and over the ankle-joint. It is bound down by firm fascia, and at the trochlea of the basal toe joints, divides into three small tendinous slips. These pass over the superior part of the second, the third, and the fourth toes, bifurcating in their course, and are inserted to the distal ones.

Shape.—Long, penniform, with a long, slender tendon.

Relations.—Immediately below the tibialis anticus.

Action.—Extends the digits as their long extensor.

=Extensor Hallucis Brevis= (Fig. 25, No. G, 4). Location.—The anterior metatarsal region, along the antero-internal edge.

Origin.—From just below the summit of the antero-internal part of the head of the tarso-metatarsus, and from the adjacent shaft below, and from the tendon of the tibialis anticus.

Insertion.—Into the process at the superior part of the bone of the bony claw of the hallux.

Shape.—Slender, thin in diameter, with a long, slender tendon.

Relations.—Superiorly, with the antero-internal edge of the metatarsus and interiorly, its tendon with the top of the hallux.

Action.—Extends the hallux.

=Extensor Brevis Digitorum.= Location.—On the anterior surface of the metatarsus.

FIG. 25.—Inner layer of muscles of the thigh of a hen. Outside view.

A. Pad of fibrocartilage or meniscus of femoro-tibial articulation. 1, Inner semi-lunar fibrocartilage. 2, External semi-lunar cartilage. 3, Anterior border.

B. Tarsal meniscus or pad of fibrocartilage.

C. Articular surface of the tarsal joint. 1, Posterior ligamentum cruciatum genu. 2, Femoral tendinous insertion of tibialis anticus. 3, Ligamentum tibio-fibulare. 4, Ligamentum interosseum. 5, Ligamentum transversum of the meniscus. 6, Anterior ligamentum cruciatum genu.

D. 1, Tibia. 2, Fibula. 3, Femur. 4, External ligamentum laterale genu.

E. Inferior surface of the tail of a hen. 1, Infracoccygis. 2, Lateralis coccygis.

F. Outside pelvic view. 1, Obturator ligament. 2, Tendon of the obturator internus. 3, Ligamentum oblongum. 4, Ligamentum capsulare. 5, Gemellus.

G. Outside view of leg of a cock. 1, Soleus. 2, Flexor longus hallucis. 3, Flexor perforans digitorum profundus. 4, Extensor brevis hallucis. 5, Extensor brevis annularis. 6, Extensor longus digitorum. 7, Tendon of the tibialis posticus.

H. 1, Transversalis abdominalis. 2, Cotyloid cavity. ]

Origin.—By a small fleshy belly to the anterior part of the proximal end of the metatarsus.