854 



OSSEOUS TISSUE. 



dened to be correct, the parietes of medullary 

 cavity should not show colour, as here absorp- 

 tion is supposed to be going on. 



From what is already known, I think that 

 the bones are coloured by the madder just in 

 proportion to their powers of imbibition, which 

 will be in inverse proportion to the amount of 

 phosphate of lime which they contain. 



As regards the growth of bone, the laws 

 common to the growth of every other tissue 

 and to the whole body will, I think, be found 

 to hold good. And the growth of these organs 

 will be found to be interstitial, pervading the 

 whole substance, though the action will be 

 more energetic at some points than at others, 

 as the neighbouring organs may require greater 

 length or breadth in one direction than in an- 

 other. 



The younger the bone the more rapid will be 

 its growth, but this law is common to all the 

 tissues. The increase of length of a long bone 

 at the epiphysis must not be confounded with 

 growth of the bone, for here, so long as car- 

 tilage connects the shaft with the epiphysis, 

 osseous tissue is being developed; whereas, in 

 speaking of the growth of bones, the increase 

 of the tissue already developed is alone meant. 



Of' the developernent of osseous tissue. As 

 the developement takes place in cartilage, and 

 as the cartilage undergoes some change pre- 

 vious to its giving place to bone, it will be 

 well to give a slight sketch of the structure of 

 temporary cartilage before going into the for- 

 mation of the more permanent tissue. The 

 rudimentary condition of cartilage may be best 

 examined in the fatal chicken, a few days 

 after the commencement of incubation. The 

 exact time for making the observation will be 

 found by taking an egg for examination every 

 six hours, commencing after the eggs have been 

 exposed to the due temperature for thirty-six 

 hours. On the first appearance of the verte- 

 bral column, which will present a semitrans- 

 parent line in the length of the developing 

 foetus, the whole must be removed with great 

 care to the field of the microscope. This part of 

 the operation requires some care, but with a little 

 management may be successfully performed. 

 I found but little difficulty in removing the 

 delicate object after adopting the following 

 plan. Having, in the first place, placed the 

 egg in a dish of water of sufficient depth to 

 cover it, letthe shell be carefully removed ; then ; 

 by moving the water with the assistance of a 

 camel's-hair brush, lake away the albumen so 

 as to leave the yelk free. The point where deve- 

 lopement is going on will then be sufficiently 

 conspicuous. At a considerable distance around 

 this the membrane of the yelk should, witli 

 a pair of sharp scissors, be cut through, and 

 carefully separated with the aid of a camel's- 

 hair brush and a pair of forceps. This having 

 been effected, the subject for examination will 

 be left on the surface of the yelk, and may, 

 with delicate manipulation with the pencil, be 

 removed to a slip of glass held near it under 

 the surface of the water. Having completed 

 your purpose so far, the glass must be raised 



very slowly from the water, so that the spe- 

 cimen may not float off, and this being covered 

 with a little thin talc or glass supported at the 

 sides, so that it shall not press upon the em- 

 bryo to be removed to the field of the micro- 

 scope. If the specimen be favourable, the 

 semitransparent line of the vertebral column 

 will under a low power appear made up of a 

 vast number of clear colourless oval cells, so 

 closely connected as to leave no appreciable 

 space between the individuals composing the 

 mass. Under a higher power, however, each 

 cell will present a definite outline with a central 

 nucleus or nuclei, and even in some nucleoli. 

 The cells give the appearance of density and 

 clearness of substance, and with their definite 

 and smooth outline present a great contrast to 

 the highly granular cells of developement that 

 surround them. In each vertebra there is 

 some show of a radiate arrangement, for many 

 cells are egg-shaped, and have their small ends 

 placed towards the centre of the growing mass. 

 At this period of the formative process the cells 

 are so close to each other that there is no space 

 for intercellular tissue. 



With the growth of the embryo the cartilage 

 advances, and its developement as a perfect 

 tissue is completed by the separation of the 

 cells from each other by the interposition of 

 an intercellular tissue. This latter is trans- 

 parent and dense, but without traces of defi- 

 nite structure, unless it be a minutely granular 

 tissue. Temporary cartilage is thus shown to 

 be composed of cells having parietes and con- 

 tents, and intercellular, (see jg. 457) or, as some 



have called it, hyaline 

 substance, through 

 which the cells or cor- 

 puscles are equally dis- 

 tributed. In cartilage 

 thus constituted, the 

 developement of bone 

 proceeds. With fhe 

 commencement of the 

 developement of bone, 

 great changes occur in 

 the arrangement of the 

 cartilage corpuscles as 

 the immediate prece- 

 dents of ossification. 

 They are no longer 

 equally distributed 

 through the hyaline 

 substance, but are 

 found arranged in pa- 

 rallel columns of varia- 

 ble lengths, in the line of the length of the bone. 

 The corpuscles forming into columns neces- 

 sarily leave intervening columns of intercel- 

 lular tissue. A notion has pretty generally 

 prevailed that the corpuscles already formed 

 marshal themselves into this order. I think, 

 however, that on further investigation it will be 

 found that each corpuscle has developed others, 

 and that they have been developed in one 

 direction only, and that towards the line 

 where osseous formation has commenced ; for 

 we find that the first perceptible change in 



Fig. 457. 



a, temporary carti- 

 lage, with the corpus- 

 cles and intercellular 

 tissue ; b, temporary 

 cartilage, with the cor- 

 puscles forming for ossi- 

 fication. 



