MUSCULAR SYSTEM 



117 



(fl. longus pollicis) (/./., Fig. 73), the differentiation of which out 

 of the common mass of the flexor profundus digitorum (f.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, i.e. 

 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 (/.&., Fig. 

 74), which is derived from the flexor 

 digitorum communis pedis. 1 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. 2 



lb 



1 In the Gorilla the flexor digitorum com- 

 munis profundus is subdivided into two portions. 



FIG. 74. MEDIAN SERIES OF THE 

 PLANTAR MUSCLES, IN THEIR 

 CONNECTION WITH THK FLEXOR 

 TENDONS. One - third natural 

 (After Rauber.) 



The ulnar portion is inserted into the fifth, the c l., tuber calcanei ; Iff., ligam. cal- 



fourth, and the middle fingers, the radial one 

 into the index finger and the pollex. Testut 

 has proved that this condition may rarely 

 occur in Man, and that it sometimes occurs 

 on both sides in the same individual. In the 

 Orang there is only a simple undivided flexor 

 digitorum communis profundus without any 

 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 quadrate 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, i.e. 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. 



caneo-cuboideum plantare ; f.l., 

 tendon of flexor longus digitorum ; 

 f.h., tendon of flexor longus hal- 

 lucis ; td., tendinous connection 

 between flexor longus and adjacent 

 tendons ; q.p'., lateral head of 

 the M. quadrati plantae flexor 

 accessorius ; q.p"., its median 

 head ; lb., Mm. lumbricales ; 

 f.V. M. flexor brevis hallucis ; 

 f.b"., M. flexor brevis minimi digiti. 



