Chap. V.] 



GENERAL HI SINOLOGY. 



69 



division. In some cases the nucleus has divided so that there 

 are two nuclei to one cell ; in others the cell has also divided, so 

 that two cells occupy one lacuna; in others a thin layer of 

 matrix divides two cells which have but recently separated from 

 one another (Fig. 25, i.). The matrix is clearly an intercellular 

 substance, answering to the cement substance in endothelium. 



FIG. 25. CARTILAGE, BONE, AND TOOTH, 



i. Cartilage, ii. Dry femur of frog in transverse section, iii. Metatarsal of 

 rabbit (transverse), iv. Lacuna of same. v. Haversian system (rabbit), vi. 

 Transverse section of part of canine tooth of cat, showing, a. enamel, &. 

 dentine, vii. Part of fang of a similar tooth, showing, a. cement, ft. dentine. 



The free surface of cartilage is invested by a membrane of 

 fibrous tissue, the perickondrium. Under favourable circum- 

 stances fine canals may be seen passing between the lacunse, and 

 from them to the perichondrium. It may be that by them the 

 cartilage is irrigated with lymph. 



Elastic and white fibro-cartilage are varieties in which the 

 matrix tends to pass into elastic or fibrous tissue. 



5. Bone. Bone sections may be prepared for microscopic 

 examination in two ways ; either (1) by grinding down (with 

 file, pumice-stone, and hone) a piece of the solid and dry bone 

 until it is sufficiently thin, and then mounting it dry ; or (2) by 



