. The American journal of anatomy. osed specificity of the epi-thelium, which is in all respects similar to that of the view of the great plasticity of epithelium of a low grade of special-ization, little importance can be attached to the argument because,both pathological histology and normal histology afford many in-stances of the transformation of a cylindrical or a ciliated epitheliuminto a stratified epithelium, as a result of the operation of simplemechanical causes, such as friction. Such an instance has been notedby Haycraft and Carlier, 89-90, in the trachea of the cat.
. The American journal of anatomy. osed specificity of the epi-thelium, which is in all respects similar to that of the view of the great plasticity of epithelium of a low grade of special-ization, little importance can be attached to the argument because,both pathological histology and normal histology afford many in-stances of the transformation of a cylindrical or a ciliated epitheliuminto a stratified epithelium, as a result of the operation of simplemechanical causes, such as friction. Such an instance has been notedby Haycraft and Carlier, 89-90, in the trachea of the cat. Hereowing to the peculiar shape of the ring of cartilage, and the modeof insertion of the muscular layer, there is a permanent fold of themucous membrane at the back of the trachea. As a result of the con-stant friction between the two layers of epithelium behind this foldthe cilia are to a large extent lost and the number of layers of cellsgreatly increased so as to bear a great resemblance to a stratified squa-mous ^ Fig. 16. Stomach of Manis javanica (modifiedfrom Weber). 144 The Cardiac Glands of i\raiiimals As regaitU the supposed contiuiiatioii of the oesophagus by the oeso-phageal groove it is found ou examination that the resemblance is butsuperficial. This has been carefully studied by Cordier, 90, who hasshown that the a^sophageal groove is produced by change in arrange-ment of the inner layer of muscle which is contrary to the rule in theoesophagus parallel to the direction of the groove. This layer becomesenormously developed at the two margins to form the lips of the grooveand reduced or completely absent in the region corresponding to thebottom of the groove. The development and functional completenessof the groove is proportional to the degree of specialization of thestomach in which it occurs, not the reverse as would be the case if itwere a persistent primitive structure. Apart frcnn the inadequacy ofthe argument advanced in its support, the hypoth
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectanatomy, bookyear1901
