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THE DENTAL ETDGE AND DENTAL GROOVE. 59

haps by the action of too powerful reagents, which led Goodsir and his
followers to describe the appearance of an open groove. The Goodsir
theory had no foundation in fact, because no such open groove ever
existed in that situation.
The various foldings found in embryonic tissue no doubt are an ex-
pression of an economic provision on the part of Nature in caring for
Fig. 40.

Section of jaw, embryo of sheep, showins; sr.iwth of enamel orc^an and dentin germ: 1, large
mass of epithelium ; '1, enamel organ ; 3, dentin germ ; 4, growing jaw.

the tissue that is to be taken up by the expansion of the parts during
its growth, as eventually they are all smoothed out. Rose's models^
show that the original inflection (stratum Malpighii) at an early stage
divides into two portions, one of which, the outer, is nearly perpen-
dicular and is intimately connected with the formation of the lip
furrow, whilst that immcHliately under consideration passes almost
horizontally backward into the tissue beneath.
At about the forty-eighth day, from the lingual side of this groove,
at a point where a tooth is to be formed, a portion of the stratum
Malpighii is found growing into the embryonic connective tissue, in
^ Models of Developing] Teeth and Jaws. By Carl Rose, M. D.