152 



PRACTICAL HISTOLOGY. 



[IX. 



and its adjacent pieces of bone (rabbit or cat). By freezing make 

 vertical sections to include the disc and its adjacent bones ; place 

 the sections for twenty-four hours in i per cent, osmic acid, wash them 

 thoroughly in water, and mount in Farrant's solution or glycerine- 



jelly. ' 



(a.) (L) Observe the decalcified bones, and between them the 

 disc (fig. 115). The bone consists, for the most part, of cancellated 

 bone, and the disc stretches between the two plates of denser bone 

 which cover the ends of the vertebrae. A thin layer of hyaline 

 cartilage exists on the surface of the bodies of the vertebrae. 



(b.) The disc itself is of considerable thickness, and consists of 

 many parallel bundles, between which, and at right angles to them, 



are other bundles cut 

 transversely, the fibres 

 of adjoining bundles 

 being arranged some- 

 times in a zigzag 

 fashion (fig. 115). In 

 these bundles are carti- 

 lage-cells, more numer- 

 ous in the central 

 bundles and fewer in 

 the outer ones. In 

 the centre of the disc 

 may be seen a more 

 pulpy tissue, the re- 

 mains of the chorda 

 dorsal is. 



(c.) Externally on 

 both sides is a ligament 

 of connective tissue 



which passes from one vertebra to the other. It gradually shades 

 into the fibres of the disc. 



(d.) (H) Observe the fibres, with a greater or less number of large 

 oval cells lying between them. The fibres can perhaps be traced 

 into the matrix of the bone. 



(e.) The cells oval and with a hyaline capsule are most numer- 

 ous in the central part of the disc, and usually there is no difficulty 

 in seeing groups of cells in the hyaline cartilage forming a thin 

 coating on the bone. The boundary-line between the disc and the 

 bone is never straight, but wavy. This can readily be made out by 

 tilting the mirror slightly. 



2. "White Fibro-Cartilage (H). Snip off a small piece of the 

 intervertebral disc of an ox or sheep or man, after hardening a small 

 portion for a day in a saturated solution of picric acid or spirit, or 



FIG. 115 V.S. Intervertebral Disc of Cat. B. Bone ; D. 

 Disc. Chroino-nitric acid fluid and osmic acid, x 15. 



