OSSEOUS TISSUE. 35 



cells (osteoclasts), lying on and eroding the newly formed bone of the osseous trabeculas. 

 (Indicate the rows of cartilage-cells, line of ossification, and other details, in PI. VI., Fig. 7.) 



L. S. PHALANX OF A FINGER FROM A HUMAN FCETUS. 



After softening, stain with picrocarmine for fifteen minutes, and mount in Farrant's 

 solution. 



EXAMINATION (L). Observe the shape of the bone under the periosteum : on each side 

 of the shaft is a triangular piece of bone, stained bright red ; the base of each triangular por- 

 tion corresponds to the surface of the shaft, the apices pointing inwards. In this piece of 

 bone are seen channels, into which vessels from the periosteum proceed. These vessels 

 are accompanied by osteoblasts into the interior of the bone, where already the central 

 part has been excavated to form primary medullary spaces. Towards the head of the bone, 

 the cartilage-cells, arranged in rows, are seen just as in an epiphysial cartilage. Under the 

 periosteum there are one or more layers of osteoblasts. 



DEVELOPMENT OF BONE (INTRA-MEMBRANOUS). 



One of the three flat bones of the skull of a foetal kitten or other animal is taken, and 

 after being hardened in picric acid it is stained with picrocarmine and mounted in Farrant's 

 solution. 



MEDULLARY TISSUE AND MARROW. 



Ordinary yellow marrow consists chiefly of fat (ninety per cent), but the spongy ends of 

 bones generally and the medullary cavity of the long bones of some animals*?^, guinea-pig 

 contain red marrow. 



PREPARATION. Take the leg-bone of a rabbit or guinea-pig, and with an axe or chisel 

 cleave it longitudinally. With the point of a knife take out a little of the red marrow, and 

 diffuse it in a drop of salt solution on a slide, and cover. 



EXAMINATION (H). Observe the marrow-cells of various shapes many of them re- 

 sembling colourless blood-corpuscles, though they contain a large clear nucleus ; others are 

 identical with colourless blood-corpuscles. Large multi-nucleated cells, many times the size of 

 a coloured blood-corpuscle, may be seen. They are the myeloplaques, osteoclasts, or giant- 

 cells, and consist of a granular mass of protoplasm, containing a large number of nuclei in 

 their interior. Dilute alcohol reveals these nuclei, and frequently causes a small, transparent, 

 bulla-like mass to appear on the side of the cell (Stirling). 



A permanent preparation of red marrow may be made by placing a piece of a long bone of 

 a guinea-pig, opened, as described above, in dilute alcohol for two days. Then put a little of 

 the marrow on a slide, and stain it with picrocarmine or logwood, and mount the preparation 

 in glycerine. 



TAIL OF A RAT DOUBLY-STAINED. 



PREPARATION. Gold chloride and an aniline dye, See p. xlvii., where this process is 

 fully described. 



EXAMINATION (L and H). The tendons are stained with gold chloride, while the bone 

 is stained of one colour and the cartilage of another. This is one of the most beautiful pre- 

 parations in the whole range of histology. 



