TIBIA AXD FIBULA 



157 



border at tlic junction of the upper and middle thirds, and is directed downwards. 

 The head of the hone receives numerous l)ranclaes from the inferior articuhir 

 arteries of the i)0])hteal, and the recurrent branches of the anterior and posterior 

 til)ial arteries. The lower extremity receives twigs from the posterior and anterior 

 tibial, the anterior peroneal, and internal malleolar arteries. 



Fig. 165.— The Tibia axd Fibula at the Sixteenth Year. 



APPEARS AT BiRTH; UNITES AT TWENTY-ONE; BUT 

 IS SOMETIMES DEUYED TO TWENTY-FIVE 



APPEARS AT THE FIRH YEAR; UNITES AT 

 TWENTY- TWO 



APPEARS AT SECOND YEAR; UNITES AT THE 

 EIGHTEENTH YEAR 



APPEARS AT THE SECOND YEAR; UNITES AT 

 TWENTY 



Ossification. — The centre for the shaft of the tibia appears in the eighth week 

 of intra-uterine life. Towards the end of the ninth month, a small earthv nucleus 

 appears in the cartilaginous head of the tibia. The nucleus for the lower ex- 

 tremity appears in the second year, and unites with the shaft at eighteen. The 

 epiphysis for the head of the bone is one of the last to unite with its shaft; this 

 event usually occurs about the twenty-first year, but may be delayed until twentv- 

 five. The tubercle of the tibia is usually ossified from the epiphysis; occasionally 

 it has an independent nucleus. 



