BONE. 



LYIL 



compactness and soliJity. The increase in girth is brought about by 

 deposition of bone at the surface underneath the periosteum. It has been 

 sometimes supposed that a formation of cartilage precedes the bone also in 



this situation ; but such is not the case, 

 for the vascular soft tissue in immediate 

 contact with the surface of the growing 

 bone is not cartilage, but a blastema con- 

 taining fibres and granular corpuscles ; in 

 fact, the increase takes place by intra- 

 membranous ossification, and accordingly the 

 Haversiau canals of the shaft are formed in 

 the same way as those of the tabular bones 

 of the skull, that is, the osseous matter is 

 not only laid on in strata parallel to the 

 surface of the bone, but is deposited around 

 processes of the vascular membranous tissue 

 which extend from the surface obliquely into 

 the substance of the shaft, (fig. LVII., a, a, in 

 transverse section); and the canals in which 

 these vascular processes lie, becoming nar- 

 rowed by the deposition of concentric osseous 

 laminae, eventually remain as the Haversian 

 canals (c, c). 



Fig. LYII. TRANSVERSE SECTION 

 OF SUPERFICIAL PART OF GROW- 

 ING METATARSAL BONE OF A 

 CALF, MAGNIFIED 45 DIAMETERS 

 (from Kolliker). 



A, periosteum ; B, vascular soft 

 tissue (subperiosteal blastema of 

 some writers) ; C, new bony 

 growth with wide spaces, a, , a, 

 some being open grooves, others 

 tubular, seen in cross section ; D, 

 more advanced and now compact 

 tissue of the shaft, with the tubular 

 spaces now nearly filled with con- 

 centric lamellae leaving Haversian 

 canals, c, f, in the centre. With 

 a higher magnifying power, in the 

 tissue B would be found fibres and 

 granular cells, and layers of these 

 cells everywhere covering the 

 osteogenic deposit on the surface 

 of the growing bone, and lining 

 the grooves and tubular spaces. 



That the ossification at the periosteal surface of 

 the bone does not take place in cartilage, may be 

 made apparent in the following manner. Strip 

 off the periosteum from a growing bone at the end 

 of the shaft, and from the adjoining cartilage 

 also, taking care not to pull the latter away 

 from the bone. A thin membranous layer will 

 still remain, passing from the bone over the 

 cartilage ; now, take a thin slice fronV the surface, 

 including this membrane with a very thin portion 

 of the subjacent bone and cartilage, and examine it 

 with the microscope, scraping off the cartilage 

 from the inside if it be too thick. It will then 

 be seen that the superficial part or shell of the 

 bone, if it may be so called, is prolonged a little 



way over the surface of the cartilage by means of 



pellucid, coarsely reticulated fibres of soft tissue (fig. LVIII. 6, c) into which the earthy 

 deposit is advancing. These osteogenic fibres are intermixed with granular corpuscles 

 or cells, but form no part of the cartilage, and they are no doubt of the same 

 nature as those seen in the intramembranous ossification of the skull. Their 

 reticulations are in most cases directed transversely, and sometimes they are little, 

 if at all, in advance of the limit between the bone and cartilage. I have observed 

 the structure here described in several bones of the (well-advanced) foetal sheep, 

 also in the human scapula, humerus, femur, tibia, and fibula, metacarpus and meta- 

 tarsus ; and, as was to be anticipated, it has since been found in all the long bones. 



Ossification having thus proceeded for some time in the shaft, at length 

 begins in the extremities of the bone from one or more independent centres, 

 and extends through the cartilage, leaving, however, a thick superficial 

 layer of it unossified, which permanently covers the articular end of the 

 bone. The epiphyses thus formed continue long separated from the shaft 

 or diaphysis by an intervening portion of cartilage, which is at last ossified, 

 and the bone is then consolidated. The time of final junction of the 



