330 MICROSCOPIC ANATOMY OF THE TEETH 



cells are also found in the neighbouring connective tissue 

 (fig- 218). 



The network in this situation is well shown in fig. 219, 

 and fig. 220 shows parallel strands of epithelium at a farther 

 distance from the root end. 



In one instance a large mass of epithelium resembling the 

 accumulations in the coronal part of the follicle was seen 

 within the connective tissue below the roots. The larger 

 strands forming the network often appear to have a limiting 



h 



os 



FIG. 221. The breaking up of the network of Hertwig's sheath by in- 

 vading connective-tissue fibres of periodontal membrane, os. Osteoblasts 

 and forming cement ; h. remains of Hertwig's sheath. ( x 250. ) 



membrane as if they were enclosed in a tube. This appear- 

 ance, however, is probably due to union of the cell walls of 

 contiguous cells. 



If the sheath is traced upwards from the root tip it is 

 seen to become less and less a continuous band, being cut 

 up and separated into isolated groups of cells by the invad- 

 ing connective-tissue bundles of the periodontal membrane, 

 which pass between them to become attached to the forming 

 cement as Sharpey's penetrating fibres ; these with the 

 osteoblasts lie to the inner side of the sheath and continue 

 the formation of the cement (fig. 221). Many of these 



