MUSCULAR SYSTEM 117 
(fl. longus pollicis) (f/., Fig. 73), the differentiation of which out 
of the common mass of the flexor profundus digitorum (/.p.) 
commences in Anthropoids, but is first carried out in Man. 
Not infrequently, however, more often in the lower than in the 
higher races, we find reversions to the primitive condition, 1. 
a more or less extensive inter-com- 
munication of fibres of, or even a 
fusion between, the flexor pollicis and 
the flexor profundus. 
This differentiation of the flexor 
longus pollicis, which finds its 
highest expression in the attain- 
ment of independent movement and 
in the greatest possible play of the 
thumb, has its parallel in that of 
the flexor longus hallucis (f-h., Fig. 
74), which is derived from the flexor 
digitorum communis pedis.’ The in- 
terchange between the fibres of these 
two muscles is so very frequent that 
it is hardly ever wanting. Further, 
all the variations observed in them 
are normally met with in Apes, even 
to the different radiations from the 
tendinous anastomosis to the toes.? Fic. 74..— MEDIAN SERIES OF THE 
PLANTAR MUSCLES, IN THEIR 
CONNECTION WITH THE FLEXOR 
TENDONS. One-third natural 
1 In the Gorilla the flexor digitorum com- 
munis profundus is subdivided into two portions. size. (After Rauber.) 
The ulnar portion is inserted into the fifth, the ¢/., tuber calcanei; Jg., ligam. cal- 
fourth, and the middle fingers, the radial one caneo-cuboideum plantare; //., 
into the index finger and the pollex. Testut tendon of flexor longus digitorum ; 
f.h., tendon of flexor longus hal- 
lucis ; ¢d., tendinous connection 
between flexor longus and adjacent 
has proved that this condition may rarely 
occur in Man, and that it sometimes occurs 
on both sides in the same individual. In the tendons; q.p’., lateral head of 
Orang there is only a simple undivided flexor the M. quadrati plante flexor 
digitorum communis profundus without any accessorius ; q.p., its median 
head; db., Mm. lumbricales ; 
f.b’". M. flexor brevis hallucis ; 
f.b"., M. flexor brevis minimi digiti. 
tendon for the thumb. This arrangement also 
has been four times observed in Man—in one 
case In a microcephalous individual. 
2 The frequent variations in the development of the caro quadrata Sylvii, and its 
occasional entire absence, find a parallel in Anthropoids. In the Chimpanzee, for 
example, the muscle is often reduced to a single little fleshy bundle, or may be 
altogether wanting, as appears to be the case in the Orang, Gibbon, and Gorilla. 
In all cases, however, the numerous variations indicate that the caro quadrata 
attained its present position secondarily, z.¢. that it must formerly have lain higher 
up on the calcaneus and the fore-leg ; and, indeed, an extension of the muscle in this 
direction has been observed. 
