THE PERIODONTAL MEMBRANE 307 



Both the blood-vessels and nerves of the membrane are 

 chiefly derived from the main trunks which are supplied to 

 the tooth-pulp. 



The final terminations of the neurofibrils bordering the 

 cement have not hitherto been satisfactorily demon- 

 strated. 



Dr. Black says that after destruction of the nerves enter- 

 ing the apical foramen, such as occurs in alveolar abscess, 

 the membrane still remains sensitive, and considers ' it 

 follows, therefore, that the nerves entering the membrane 

 through the walls of the alveolus are sufficient for the 

 maintenance of the sensory functions '. Black describes 

 nerve bundles entering the wall of the alveolus by way of 

 the Haversian canals, but he does not actually demonstrate 

 any such nerve supply, and although nerve fibres enter the 

 bone in company with the arteries we do not think it has 

 ever been shown that they have any distribution without the 

 bone, but are supplied to the coats of the arteries. 



The same author in his work on the Periosteum and Peridental 

 Membrane devotes a chapter to the description of lymphatics 

 in the membrane, but there can, we think, be little doubt 

 that the structures which he describes as lymphatics, and 

 which he compares to the Peyer's patches of the small 

 intestine, are not glands but the epithelial remains of the 

 sheath of Hertwig, present in all teeth. 



The remains of the epithelial sheath are seen as isolated 

 collections of epithelial cells lying in a more or less complete 

 row at a little distance from the cement. 



The continuous sheath which extends downwards during 

 the formation of the root becomes cut up by the invading 

 fibrous bundles, and in many places disappears ; but where 

 the membrane is not very dense, remains as rounded or 

 elongated collections of cells which have a strong resem- 

 blance to glandular tissue. 



The limiting membrane which Black describes appears to 

 be the result of the union of the cell walls of contiguous cells, 

 and is very marked in the network of epithelial cells forming 

 the sheath of Hertwig beneath the forming roots of the 

 teeth, as described on another page. 



Fusiform connective-tissue cells are everywhere present 



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