156 SKELETON. 



leaves the reader to infer, that it was a circumstance which had 

 arisen from a violent hemicrania, with which the patient had 

 been seized when he was advanced in life. Diemerbroek found, 

 in a woman of forty, the anterior fontanel not ossified. Bauhius' 

 wife, aged twenty-six, had the sutures not yet closed. Indeed, 

 there is no deficiency of well authenticated similar instances, 

 more of which it will be unnecessary to adduce. It may be ob- 

 served here, that when from congenital hydrocephalus, attended 

 with much extension of the brain, the bones of the cranium are 

 compelled to grow beyond their usual diameters, they are un- 

 commonly thin, and the diploic structure is very imperfectly 

 developed : which will account for their separation at any period 

 of life, from the fastening being so slight. 



SECT. II. OF THE DIPLOIC STRUCTURE OF THE CRANIUM. 



The bones of the cranium, in the adult, consist of an external 

 and of an internal table; united by a bony reticulated or cellu- 

 lar substance, which does not manifest itself very distinctly till 

 two, three, or even more years are passed, by the infant. The 

 internal table of the skull is thinner and more brittle than the 

 external, and has obtained, from that cause, the name of vitreous 

 table. 



The cells of the diploic structure are not to be confounded 

 with the large sinuses that exist in the frontal, the temporal, and 

 the sphenoidal bones. They are formed under different circum- 

 stances, and do not communicate with them. The sinuses are 

 lined by a mucous membrane, whereas the lining membrane of 

 the cells of the diploe corresponds with the internal periosteum 

 of other bones. I have a preparation now before me, in which 

 the diploic structure of the os frontis exists between its sinuses 

 and the external table of the bone: in the same head, a similar 

 circumstance existed in regard to the temporal bone; from which 

 we infer that the diploic structure, in these places, is caused to 

 recede, and even to be partially obliterated, when the develop- 

 ment of the sinus commences, which is not until some time af- 

 ter the evolution of the diploic structure. The sphenoidal bone, 

 when fully evolved in its body, is a remarkable instance of the 

 recession of diploic structure for the purpose of forming a sinus. 



