178 PROCEEDINGS OF THE- ANATOMICAL AND ANTHROPOLOGICAL 



ternal to the bone, becomes the pericranium, the layer, internal to 

 the bone, becomes the " dura mater," or endocranium, while the un- 

 ossified portions of the .capsule, between the edges of the growing 

 1 tones, is left as the membranes of the fontanelles and sutural liga- 

 ments ; and at the base of the skull, part of the cartilage remains as 

 the cartilaginous plates, between the basioccipital and basisphenoid, 

 and between the basisphenoid and presphenoid. Synostosis of the 

 two portions of the body of the sphenoid normally occurs before birth, 

 while the cartilage between the occipital and sphenoid bones does not 

 become completely ossified till after the twentieth year. Growth in 

 length at the base of the skull takes place at these cartilages ; thus, if 

 premature union of the bones takes place, there will be shortening at 

 the base of the skull. This shortening of the base is usually accom- 

 panied by compensatory enlargement in other parts. 



After birth the growth of the brain and skull is very rapid, the 

 individual bones forming the skull enlarging by a growth which takes 

 place at their edges, and also, it is said, by a deposition of new bone 

 upon the surface and absorption of bone from within. Accompanying 

 this increase in the size of the skull there is a gradual Hattening of 

 the bones, the curvature of the separate bones lessening as they come 

 to form segments of a larger sphere. Thus the frontal and parietal 

 eminences, which are well marked at birth, become less prominent, 

 Mud sometimes quite indistinguishable in the adult. The occasional 

 prominence of these eminences in the cuboidal form of skull, which is 

 sometimes met with in the adult, may therefore be regarded as a 

 persistence of a foetal condition. 



Finally, with the advance of age, and at a somewhat variable 

 period, obliteration of the sutures between the bones takes place, and 

 the bones of the skull become fused into one continuous whole. 



The cause of this union of the bones is, so far as I know, unex- 

 plained ; certain of the sutures, such as that in the occipital bone 

 between the interparietal and the supraoccipital, and the suture 

 between the two halves of the frontal bone, namely the metopic, or 

 interfrontal suture, close early, long before the growth of the skull is 



