304 HUMAN EMBRYOLOGY AND MORPHOLOGY. 



the external tubercle of that bone. It may remain separate and 

 form the os trigonum (Fig. 247). 



3. Ulnare becomes the cuneiform in the hand ; the os calcis in 

 the foot. During the fibrous and early cartilaginous stages in the 

 development of the human tarsus, the os calcis is in contact with 

 the fibula. In the hand the ulnare and intermedium are bound 

 by fibrous bands to the ulna (Fig. 246); these bands assist to 

 form the triangular fibro-cartilage. 



4. Carpale or Tarsale I. becomes the trapezium in the hand, 

 the internal cuneiform in the foot. In the prehensile foot of apes, 

 the hallucial articular surface is directed inwards for the move- 

 able big toe. This is also the case during the foetal development 

 of the human foot (Leboucq). At no period of development is 

 the hallux of man directed inwards and separated from the other 

 toes. In man the great toe resumes a primitive position and 

 its metatarsal lies parallel with those of the metatarsal series. 



5. Carpale or Tarsale II. forms the trapezoid in the hand, the 

 middle cuneiform in the foot. 



6. Carpale or Tarsale III. forms the os magnum in the hand, 

 the external cuneiform in the foot. 



7. Carpale or Tarsale IV. and V. have united in both hand and 

 foot to form the unciform and cuboid. This union is seen in 

 mammals generally. In the cat and carnivores the scaphoid and 

 semilunar unite together. 



The Os Centrale is situated between the first and second rows 

 of the carpal or tarsal bones (Fig. 246). In the foot it forms the 

 scaphoid — a bone which plays an important part in the formation 

 of the plantar arch — but is yet remarkably late in beginning to 

 ossify, viz., about the 3rd year. It appears in the membranous 

 stage of the human carpus, but at the end of the 2nd month it 

 has joined the dorsal and distal aspect of the scaphoid of the hand. 

 It may be occasionally detected as a tubercle on the dorsal aspect 

 of the scaphoid or even as a separate bone. It is a separate bone 

 in the carpus of all primates except the gorilla, chimpanzee, and 

 man. There are two centralia in lower vertebrate forms. 



The Pisiform (ulnare laterale of Forsyth Major) is of doubtful 

 nature. It is possible that in a very early stage of the evolution 

 of mammals there were more than five digits — one behind the 

 little finger — post minimi digiti; and another on the radial side 



