258 MANUAL OF HISTOLOGY. 



If we remember, also, that the cavity in question of a fully grown 

 bone occupies more space than is taken up by the entire bone at an 

 earlier period of life, we see that the whole of the primitive osseous 

 tissue must have fallen a prey again to absorption, and the mature bone 

 consist of osseous substance formed only from the periosteum. The 

 Bayers supplied by the latter are the general lamellae, as is easy of com- 

 prehension, and as may be seen in every section (fig. 233). Of course, 

 from what has just been stated, it will be remarked that the oldest of 

 them that are present become eventually medullary lamellae, bounding 

 the great medullary cavity. 



In regard to the details of this process of re-solution, to which we 

 have been obliged to allude so frequently, but little was known until very 

 lately. From Koelliker's very extensive investigations, it would appear 

 that modified multinuclear cells spring from Gegenbaur's osteoblasts, 

 attaining considerable dimensions in some cases : these are closely applied 

 to the undulating eroded borders of the " lacunae of Hmoship" of the 

 dissolving bony tissue. 



These multinuclear " giant cells " (discovered, to be sure, years ago) 

 have been named "ostoklast" by Koelliker, who ascribes to them a 

 power of dissolving the bone. I have not the faintest belief in their 

 possessing this latter property. 



It is improbable that, at the same time that this takes place, the bone- 

 corpuscles formerly enclosed in ground-substance are set free, and, becom- 

 ing medullary cells by retrograde metamorphosis, provide for the necessary 

 increase in the bulk of the marrow. 



In short and flat bones, on the other hand, a certain amount of the 

 original bony tissue, sometimes greater, sometimes less, remains, of that, 

 namely, which w T as formed at the expense of the cartilage. 



REMARKS. The investigations of L. Oilier are to be found in the Journ. de la 

 vhysiologie, Tome ii. p. 1, 170, 468, and T. iii. p. 88, as well as in the Gazette me~di- 

 cale, 1859, Nr. 37, and 1860, Nr. 12. A resume of these works, with new experi- 

 ments, appears in a new two- volume work of the same author, Traitl experimental et 

 clinique de la rfytntration des os et de la production artificielle du tissue osseux. 

 Paris, 1867. 



1^9. 



We now come to the origin of secondary bones, or, better expressed, 

 of those not previously moulded in cartilage. To these belong, as is 

 usually received, the flat cranial bones, with the exception of the under 

 part of the occipital, which is modelled first in cartilage ; further, the 

 upper and lower jaw, the nasal, lachrymal, and palate bones, the vomer, 

 zygoma, and, finally, the inner leaf of the wings of the sphenoid and 

 Cornua splienoidalia (Koelliker). These spring up outside of the primor- 

 dial skull from circumscribed spots, which spread out subsequentlv. 

 gaining rapidly in superficial extent. Here we first meet with a (true) 

 osseous nucleus, which grows out in all directions, forming a network of 

 bony bands and needles (Kalkbalkchen and Kalknadelri), which are lost 

 in the adjacent soft tissue. It is easy to recognise here, also, the simi- 

 larity of the osteogenetic process to that in other parts of the system, and 

 to see that these bony bands are covered by a layer of osteoblasts 

 (fig. 246). 



Much difference of opinion still prevails as to the nature of this original 

 tissue, as also of that of the corresponding subperiosteal stratum ; one 

 party regarding it as an undeveloped connective-tissue substance, and not 



