143 



which serves to connect these two membranes in the intervals 

 of the bones, and also the bones themselves ; for it passes from 

 the edffe of one bone to that of another. It is to be observed, 

 that those bones, which form the posterior part of the vault, have 

 extended tlieir growth farther than those, which constitute the 

 anterior part. Hence the smaller size of the occipital, when 

 compared with the frontal fontanella: a fact observed by Mor- 

 gagni,* and considered by him to depend on the cerebellum 

 requiring to be well defended during parturition. 



These facts, respecting the changes in structure, which the 

 walls of the cranium undergo at different periods, prove, that 

 the ossification of the base advances more rapidly than that of 

 the vault. This does not, on a first view, seem to accord with 

 the observations just made on the growth of the dimensions of 

 these two parts of the cranium, compared with each other. It 

 has been already remarked, that the base is much slower in 

 developing itself than the vault ; but this observation only related 

 to the growth in dimensions, not in structure. It may, however, 

 appear extraordinary, that there should not be a connexion be- 

 tween the growth of the structure, and the growth of the di- 

 mensions. The cause of this want of connexion is, however, on 

 reflection, very evident. The development of the cranium in 

 dimensions must keep pace with the development of the dimen- 

 sions of the brain; but the growth in structure is connected 

 with the necessity, which the different parts of the brain have 

 for defence ; therefore, as the dimensions of that part of the brain, 

 which corresponds to the vault of the cranium, grows with 

 greater rapidity, the same must occur with respect to the corres- 



• Adversar: Anat. 11. Animad. 32. 



