306 HUMAN EMBRYOLOGY AND MORPHOLOGY. 



much the lower ; a growth upwards of the inner border 

 causes the astragalus and foot to rotate outwards (Lazarus). 



^-^___—- right astrag. at birth 

 neck long anrf, ( ..•■•■V"--, 

 bent inwards r~Y\ \ -f- r '9 ht astra 3- of adult 



tib. artic. surface^fw" — ' )N. 



Flo. 248. — The Foetal and Adult (in dotted outline) Forma of the Astralagus 



contrasted. 



(6) The bones on the inner side of the foot, particularly the 

 scaphoid and internal cuneiform, grow more rapidly than 

 those on the outer side of the foot — especially after 

 birth. This tends to evert the foot and also to produce 

 the longitudinal arch. 



(c) A special evertor of the foot is produced — the Peroneus 

 tertius — a muscle peculiar to man. It is developed from 

 the outer and lower fibular fibres of the extensor longus 

 digitorum and represents part of the tendon of that 

 muscle to the 5th toe. The peroneus brevis and longus 

 may also assist, especially the latter, which in apes is 

 a grasping muscle, acting as a flexor of the metatarsal 

 bone of the hallux. 



(2) The tarsal bones of the human foot — especially the astra- 

 galus and os calcis — are of great size when compared with the 

 tarsal bones of other primates ; while the digital or phalangeal 

 elements, except in the case of the great toe, which is relatively of 

 great size, have undergone retrogression. This is especially the 

 case in the human little toe ; some of its muscles are not in- 

 frequently fibrous, and the terminal phalanx may not be separated 

 from the middle phalanx. The terminal phalanx is the last to be 

 differentiated in development of the fingers and toes. 



(3) The plantar arches, both longitudinal and transverse, are 

 produced. The arch of the foot is a human character. At birth 

 the child is flat-footed ; the head of the astragalus touches the 



