THE CRANIUM. 165 



close before or about the time of birth. Separate ossifications, 

 which become Wormian bones, are often developed in the primi- 

 tive capsule of the skull at those three fontanelles and thus close 

 them. The anterior superior fontanelle, at the bregma, cannot be 

 distinctly felt during life after the first year (Warner), but it is not 

 completely closed until the second year is nearly over. This 

 fontanelle is lozenge-shaped, being bounded by four bones, viz., 

 the two parietals and two frontals. The bregmatic or anterior- 

 superior and lambdoid or posterior-superior fontanelles are median 

 and common to both parietals. 



The membrane-formed bones consist at first of a thin lamella 

 of osseous fibres radiating out from the point at which ossification 

 commenced. The osteoblasts beneath the pericranium on the 

 outer surface of the lamella and the dura mater on the inner 

 surface deposit bone, and by the 5th year an outer and inner 

 table, with deploic tissue between, are developed. Into the 

 diploe of the frontal bone protrude the growing buds of the two 

 frontal sinuses. As the brain expands new bone is formed at 

 the sutures to increase the capacity of the skull, but the opera- 

 tion of craniotomy to allow the expansion of a confined brain, 

 by the formation of a new suture, is founded on a wrong 

 principle. Expansion of the cranial cavity takes place princi- 

 pally by a deposit on the outer table and an absorption from 

 the inner ; for this manner of growth, sutures are unnecessary. 

 The synostosis of the sutures does not necessarily prevent growth ; 

 synostosis of the skull bones occurs only when the brain has 

 ceased to expand. If the brain of the infant is arrested in its 

 growth, premature ossification of the sutures occurs, the condition 

 of microcephaly resulting therefrom. In hydrocephalus, when the 

 ventricles become enormously dilated, the membranous capsule of 

 the cranium expands so quickly that the process of ossification 

 cannot keep up with its rapid growth. Hence in hydrocephalus 

 the fontanelles are enormous. The cartilaginous part of the skull 

 is scarcely affected in this disease. The membrane-formed part 

 of the skull is liable to diseases which do not affect the cartilage- 

 formed part. The dura mater is very adherent to the bones 

 formed in cartilage. 



Development of the Cartilaginous part of the Skull. 

 (1) The Occipital Bone. — The occipital bone is developed from 



