MUSCLES OF THE THORACIC LIMBS. 181 
Action indicated by the name. 
M. flexor sublimis digitorum (or perforatus).—-This muscle 
is in two parts, which are given a common name only because 
of the similar structure and insertions of their tendons. 
The ulnar part (Fig. 77, x) is a conical muscle taking 
origin from the outer surface of the tendon and muscle of the 
palmaris longus and from the adjacent ligament. It gives rise 
to two or three tendons (Fig. 88, 4) which arise from distinct 
slips of the muscle; these pass to the ulnar two or three digits: 
That passing to the fourth or fifth digit receives an accessory 
slip from a small mass of fibres attached to the transverse liga- 
ment on the radial side of the palmaris tendon. 
The radial part is a small flat triangular muscle which 
takes origin from the outer surface of the tendon formed by the 
junction of the tendons of the first and second parts of the flexor 
profundus. It divides into two slips, each giving rise to a 
tendon. These tendons (Fig. 88, 4') pass to the second and 
third digits. That to the third digit may divide into two, one 
of which goes to the fourth digit. 
Each of the four tendons (Fig. 88, 4 and 6’) is perforated 
by a tendon of the flexor profundus (Fig. 88, c) as it passes 
through the fibrous pulley-ring at the base of the first phalanx. 
It. then continues beneath the flexor profundus tendon through 
the second pulley-ring (2) and is inserted into the base of the 
second phalanx. 
Relations.—Outer surface of the ulnar part with the integu- 
ment; inner surface with the palmaris longus (Fig. 77, 5). 
Outer surface of the radial part with the palmaris longus; inner 
surface with the flexor profundus. 
Action.—Flexor of the second phalanx of digits 2-5. 
-M. flexor profundus digitorum (or perforans).—This arises 
by five heads, the tendons of which join one another at the wrist 
to make the strongest and deepest of the flexor tendons. 
The first or ulnar head has origin (Fig. 87, g) from the dor- 
sal half of the medial (radial) surface of the ulna from the proximal 
lip of the semilunar notch to within a centimeter of the styloid 
process. Its fibres converge to a large flat tendon which forms 
the lateral (ulnar) and superficial part of the common tendon. 
