334 SPECIAL HISTOLOGY. 



and are connected merely by a fibrous membrane, the continuation of 

 the periosteal lamella of each, and which is united on the internal 

 aspect with the remains of the membranous cranium of the embryo, 

 and with the dura mater. The bones then continue to grow towards each 

 other, and at last constantly advancing in the above-described continua- 

 tion of the periosteum, come very nearly into contact at the frontal and 

 sagittal sutures; there remains, however, for a long time one large vacuity, 

 in particular, between them, — the anterior fontanelle, — but which closes 

 in the second year after birth ; whilst at the same time, the bones, 

 which, up to this period, adjoined each other with a straight line of 

 juncture, send out interdigitating tooth-like processes, till ultimately, 

 when their blastema is wholly consumed, they continue united only by 

 the remains of the periosteum (the sutural cartilage, as it is termed, or 

 better, the sutural ligament), but which also is capable of becoming 

 ossified sooner or later, and, indeed, invariably first on the inner aspect 

 of the suture, where the tooth-like processes are very little developed. 

 The changes of form in the entire bones during their development are 

 very remarkable, and have hardly been attended to. If a parietal 

 bone, for instance, of a foetus or new-born child, be compared with that 

 of an adult, it will be found that the former is much more curved, and 

 in no way at all represents a piece cut out of the middle of the latter. 

 The adult parietal bone consequently must have undergone a very 

 important alteration in the curvature of its surfaces, and this, as 

 mechanical conditions are out of the question, can only have been 

 effected by an unequal deposition of bone internally and externally, in 

 the middle and at the borders ; or by deposition on the one side and 

 absorption on the other. That unequal deposition does actually occur, 

 is seen, for example, in the juga cerehralia and impressiones digitatce, 

 the sulci meningei, &c. ; but it appears to me, that the whole matter 

 cannot be understood, unless we assume that heal absorptions also take 

 place in certain situations. How otherwise can be explained the in- 

 crease in breadth of the superior orbital ridge, the increase of distance 

 between the frontal eminences, even after the ossific union of the two 

 portions of the frontal bone, the change of form of the lower jaw (the 

 greater distance between the coronoid processes and the mental spine, the 

 alteration in its curvature, the partial removal and renewal of the alveola'), 

 &c.? We have already seen, that in the other bones, also, something 

 of the kind must be presumed to take place, and, consequently, cannot 

 hesitate to admit it in the present case, although the particulars of the 

 process be unknown. That this process occurs in the interior of the 

 secondary bones has been already mentioned. The formation of the 

 diploe, which becomes more evident in the tenth year, is to be referred 

 to it, as is also that of the frontal sinuses, and antrum Highmorianum, 

 which however does not take place till a later period. 



