330 SPECIAL HISTOLOGY. 



and chemical relations of the matrix of these two forms of osseous 

 tissue have not as yet been determined. On the other hand the bone- 

 laeunge of both kinds of tissue do not present the least difference. 



106. Bones not primarily cartilaginous occur, in Man, only in the 

 cranium. They originate outside the primordial cranium, between it 

 and the muscular system, and thus within the structure constituting the 

 vertebral system. They by no means exist as membranous and cartila- 

 ginous capsules on the first appearance of the cranium, their formation 

 not commencing till after that of the primordial cranium, from a secon- 

 dary blastema, whence, in contradistinction to the other primary bones, 

 the formative material of which exists prior to the commencement of 

 ossification, they are termed secondary bones or, also, because in most 

 places they are in contact with portions of the primordial cranium 

 covering or overlaying bones (belegknochen). To this class belong, the 

 upper half of the expanded portion of the occipital bone, the parietal, 

 and frontal bones, the squamous portion and tympanic ring of the tem- 

 poral bone, the nasal, lachrymal, malar, and palate bones, the upper and 

 lower jaw, the vomer, and apparently, the internal lamella of the ptery- 

 goid process of the sphenoid, and the cornua sphenoidalia. The blastema 

 of these bones, which differs from that of the primary bones, in its being 

 successively developed in a membranous matrix, simultaneously with the 

 process of ossification, not existing previously in any considerable quan- 

 tity, presents essentially, exactly the same conditions as that of the 

 periosteal layers, and is also ossified in precisely the same way. 



The notion that certain cranial bones, in man and the Mammalia, are 

 not developed from cartilage, is by no means new, although the morpho- 

 logy of the question was first established by Rathke, Reichert, Jacobson, 

 and myself; and its histology by Sharpey and myself. But with respect 

 to the latter subject, a controversy still exists as to the true nature of 

 the ossific blastema (as also, of that of the periosteal layers), whether 

 it be a kind of connective tissue, as I believe, or a sort of cartilage, as 

 Reichert and A. Bidder assert, with respect to which more will be found 

 in my "Mikroskop. Anat." pp. 374, 375. 



107. The secondary cranial bones, all, in the first instance com- 

 mence in the form of a minute, elongated, or rounded, osseous nucleus, 

 consisting of a portion of fundamental substance or matrix, with a few 

 lacunae, and which is surrounded by a small quantity of soft blastema. 

 How this nucleus originates has not yet been observed, although from 

 the way in which its growth proceeds, it might be assumed with certainty, 

 that shortly previous to its first appearance, a minute lamella of the 

 soft blastema is formed in the situation of the future nucleus, which 

 lamella spreading from a single point, becomes ossified by the addition 



