BONE. 51 



from the underlying vessels proceeding from the periosteal tissue. It is to 

 these vessels, and to the cavities or tubes which they form for themselves as 

 they proceed inwards, that the origin of the Haversian canals is due. 



The origin of the lacuna and of the bone-cells which fill them is still a 

 matter of dispute. Kolliker, Virchow, and many other anatomists, maintain 

 that in the intra-cartilaginous ossification they are developed directly from the 

 cartilage-cells, the investing membrane of which ossifies and forms the bony 

 lacuna, while its nucleus is developed into the bone-cell. Others, as Dr. 

 Sharpey, H. Miiller, and Eollett, believe that the cartilage-cells, after becoming 

 developed into the " osteoblasts," above described, and shown at 6, Fig. 20, 

 become dissolved, and shed their granular contents to form the bony matrix, 

 while the lacunae and bone corpuscles are developed from the granular masses, 

 which are seen below g in the figure, and which are furnished, according to 

 these authors, from the vessels of the periosteum or perichondrium. If this 

 view be correct, the intimate process is the same in all forms of ossification. 



Thus far, then, we have followed the steps of a process by which a solid 

 bony mass is produced, having vessels running into it from the periosteum, 

 Haversian canals in which those vessels run, medullary spaces filled with foetal 

 marrow, lacunre with their contained bone-cells, and canaliculi growing out of 

 those Iacuna3. 



This process of ossification, however, is not the origin of the whole of the 

 skeleton, for even in those bones in which the ossification proceeds in a great 

 measure from a single centre, situated in the cartilaginous diaphysis, a con- 

 siderable part of the original bone is formed by intra-membranous ossification 

 beneath the perichondrium or periosteum. Kolliker (following H. Miiller, and 

 referring to an observation of Howship to the same effect, made so long ago 

 as 1819), describes the first rudiment of a long bone as having the form of a 

 tube, surrounding the primordial cartilage; thus showing that the intra- 

 membranous ossification of the outer part of the bone from the periosteum 

 even precedes the intra-cartilaginous development of its interior from the 

 "ossific centre." Also, a great part of the increase in girth of the bone takes 

 place by bony deposit from the deeper la}^er of the periosteum. This process 

 is now acknowledged to belong to the intra-membranous form of ossification. 

 Thus even in long bones only a portion of their tissue is formed by intra-carti- 

 laginous ossification. 



The shaft of the bone is at first solid, but a tube is gradually hollowed out 

 in it by absorption around the vessels passing into it, which becomes the 

 medullary canal; and as more and more bone is deposited from the periosteum, 

 so more and more is removed from around the medullary membrane, until at 

 length the bone has attained the shape and size which it is destined to retain 

 during adult life. As the ossification of the cartilaginous diaphysis extends 

 towards the articular ends it carries with it, as it were, a layer of cartilage, or 

 the cartilage grows as it ossifies. During this period of growth the articular 

 end, or epiphysis, remains for some time entirely cartilaginous, then a bony 

 centre appears in it, and it commences the same process of intra-cartilaginous 

 ossification, but this process never extends to any very great distance. The 

 epiphyses remain separated from the shaft by a narrow cartilaginous layer for 

 a definite time. This layer ultimately ossifies, the distinction between shaft 

 and epiphysis is obliterated, and the bone has assumed its completed form and 

 shape. The same remarks also apply to the processes of bone which are sepa- 

 rately ossified, and called apophyses. 



The intra-cartilaginous ossification, and the growth by means of epiphyses, 

 are usually described from the long bones; but almost all the bones of the 

 body are primarily laid down in cartilage (see note, p. 49); and a great many of 

 the flat and short bones grow by means of epiphyses, as will be seen in the de- 

 tailed description of each, given in the body of the work. 



The medullary spaces which characterize the cancellous tissue are produced 



