THE LIMBS. 



311 



on the ulnar side ; (3) a contrahens or adductor muscle (always 

 absent in the middle digit). The ten short flexor muscles 

 form a deeper sheet than the four contrahentes. Of this form 



pi. inter. 3 



opponens and j fior. inter. 4 



[flex. breu. mm. 

 digiti 



1st meta-tarsal 



tib. head Hex. 

 brev. hal. 



contrah V. contrah IV. contrah II. 

 deep plant, nerve 



j c6ntrah I & 

 [adduct hal. / 



aod. halluc 



Fig. 250. — The Morphology of the Short Muscles of the Digits. The Muscles shaded 

 are those of the ape's hand or foot ; the positions of the corresponding muscles in 

 - the human hand or foot are indicated by dotted outlines. 



the arrangement of the short muscles in the human hand is 

 a derivative. The remnants in the human hand and foot of 

 the contrahentes are: (1) The adductors of the 1st digit (pollex 

 or hallux) ; (2) fibrous remnants of the others occur over the 

 deep plantar or carpal arch (Fig. 250). The short flexors in 

 man have become (1) the seven interossei ; (2) the fiexores 

 breves (ulnar and radial) and opponens of the first digit ; (3) 

 the flexor brevis and opponens of the fifth digit (see Fig. 250). 

 The ulnar flexors of the thumb and great toe are absent or 

 fibrous. 



(12)' The Pyramidalis is often absent in man or vestigial. It 

 is the tensor of the linea alba. 



(13) Eemnants of the extensors and flexors of the tail may 

 occur between the sacrum and coccyx (page 136). 



(14) The Coccygeus is vestigial; its superficial part forms the 

 small sacro-sciatic ligament. 



(15) Fibres of the biceps of the thigh may be followed into the 

 great sacro-sciatic ligament. This ligament, which is almost peculiar 

 to man — in other primates it is quite thin and slender — may con- 

 tain fibres derived from the caudo-femoral group of muscles, such 

 as the tenuissimus, a long strap-like muscle which passes from the 

 coccyx to the femur and leg in lower mammals. The sacro- 



