348 GENERAL PRINCIPLES 



the skull were enlarged by the removal of material from the 

 inner surface of the skull bones. The end is accomplished in 

 another way. The skull is composed of many pieces, which are 

 fitted together in a peculiar way. The seam, or suture, along 

 which two bones join is not an even line or smooth joint; it is an 

 extremely sinuous line which effects a dovetailing of the two 



FIG. 216. Skull of a human embryo at time of birth. The bones are still 

 separated by seams of cartilage and membrane. The broad unossified space is 

 called a fontanelle. In the figure the radiating lines on the parietal bone (large 

 bone on the left) indicate the original centre of ossification and the direction of 

 growth. 



bones in a way to produce a very firm joint. The suture dis- 

 appears at maturity by the complete fusion of the bones, but 

 until the end of the growth period the suture is an open joint, in 

 which material is being added to the bones of both sides. The 

 skull, as a whole, therefore, expands by interstitial growth, while 



