177. For the same reason, two muscles are provided for flexing, while only one is provided for extending the fingers. The flexors, bulky, thick, and strong, are placed on the fore part of the fore-arm (fig. LXXXIV.). The first, named the superficial flexor (fig. LXXXIV. 1), about the middle of the arm, divides into four fleshy portions, each of which ends in a slender tendon (fig. LXXXIV. 1). As these tendons approach the fingers they expand (fig. LXXXIV. 1), and when in apposition with the first phalanx, split and form distinct sheaths for the reception of the tendons of the second flexor (fig. LXXXIV. 3). After completing the sheath, the tendons proceed forward along the second phalanx, into the fore part of which they are implanted, and the chief office of this powerful muscle is to bend the second joint of the fingers upon the first, and the first upon the metacarpal bone. Its action is assisted by a second muscle, called the deep or profound flexor (fig. LXXXIV. 2), because it lies beneath the former; or the perforans, because it pierces it. Bulky and fleshy, this second flexor, like the first, about the middle of the arm, divides into four tendons, which, entering the sheaths prepared for them in the former muscle (where the tendons are small and rounded for their easy transmission and play), pass to the root of the third phalanx of the fingers into which they are implanted (fig. LXXXIV. 3). [Illustration: Fig. LXXXIV. View of the flexor muscles of the fingers. 1. The superficial flexor, divided and turned aside, to show, 2. the deep flexor; 3. sheaths for the tendons of the deep flexor, formed by the splitting of the tendons of the superficial flexor; 4. the anterior annular ligament, divided and turned aside.] 118. The muscle that extends the fingers, called the common extensor, is placed on the back part of the fore-arm (fig. LXXXV.), about the middle of which it divides into four portions which terminate in so many tendons (fig. LXXXV. 2). When they reach the back of the metacarpal bones, these tendons become broad and flat, and send tendinous expansions to each other, forming a strong tendinous sheath which surrounds the back of the fingers (fig. LXXXV. 2). These tendinous expansions are inserted into the posterior part of the bones of the four fingers (fig. LXXXV. 2); and their office is powerfully to extend all the joints of all the fingers (fig. LXXXV. 2).