OSTEOLOGY. 7 



Ossification appears first in the clavicle and inferior maxilla 

 (from fifth to seventh week) and last in the pisiform bone 

 (twelfth year). The epiphyses ossify from birth and unite from 

 the age of puberty on to maturity, in reverse order to the ap- 

 pearance of ossification, being regulated, apparently, by the direc- 

 tion of the nutrient artery in the upper extremity toward the 

 elbow and in the lower extremity from the knee. The only 

 exception to this rule is the lower end of the fibula, which ossifies 

 and also becomes united before the upper (vide Table of Ossifi- 

 cation). In bones with only one epipbysis the artery is directed 

 toward the other extremitv. 



1, frontal eminence; 2, superciliary ridge; 3, supra-orbital arch; 

 4, external angular process; 5, internal angular process; G, supra- 

 orbital notch; 7, nasal eminence; 8, temporal ridge; 9, nasal spine. 



Growth of Bones. Long bones grow in thickness from the 

 periosteum and in length from the cartilage between the epiph- 

 yses and the shaft near the extremities. The medullary cavitv 

 is at first solid and grows by absorption of the cancellous tissue 

 by the giant cells, or osteoblasts. 



Flat bones grow in thickness from the periosteum and in 

 surface from the borders. Short bones grow from the centre 

 or centres of ossification in all directions. 



THE CRANIAL BONES. 



The cranial bones are eight in number: 



1 Frontal, 2 Temporal, 



2 Parietal, 1 Sphenoid, 

 1 Occipital, 1 Ethmoid. 



