THE TONGUE. 207 



only the mode of development of the teeth, but also 

 that of the hair, the bone of the lower jaw (which 

 ossifies in the connective tissue around Meckel's car- 

 tilage), the tongue, and many other parts. The pre- 

 paration is as follows: The foetuses or young animals 

 are decapitated, and the heads dropped into a large 

 beaker of one-sixth per cent, chromic acid. After a 

 week's time, during which the liquid is now and 

 then stirred, they are transferred to weak spirit, and 

 in twenty -four hours to strong spirit. After being 

 in this a day or two they are ready for cutting. 

 Either the lower jaw is removed and imbedded sepa- 

 rately, or the whole head is placed in the mould, and 

 both jaws are cut simultaneously. The sections are 

 to be stained, some with logwood, some with carmine 

 solution (made by dissolving two grammes of carmine 

 in a few drops of ammonia, and diluting with water 

 to one hundred cubic centimetres). The stay in 

 chromic acid may not have been long enough to 

 remove all the earth from the partly developed bones 

 and teeth, but what still remains is so small in 

 amount that it will not prevent a thin section being 

 made. The earlier stages in the development of the 

 teeth may be perhaps seen in the molar region ; the 

 later stages comprising the development of the dental 

 tissues, especially the dentine and enamel, may be 

 studied in the much more advanced incisors, w r hich, 

 as just pointed out, extend backwards in these ani- 

 mals through the greater part of the length of the 

 jaw. 



THE TONGUE. 



Preparation 7. Small portions of this organ 

 from different parts are hardened in two per cent, 

 bichromate of potash (fourteen days), and subse- 

 quently in spirit, and are imbedded, so as to cut 

 vertically to the surface of the mucous membrane. 

 The sections are stained with logwood, and mounted 

 in dammar varnish. A double staining with picric 



