1888.] 



NATURAL SCIENCES OF PHILADELPHIA. 



261 



Most variations in human anatomy are said to be reversions. 

 While this method is a most valuable one it has a limited use when 

 applied to the study of the rugse, excepting in the instance of the 

 broken rugse, and even here the comparison is not exact. 



The human rugse derive their peculiarity from two causes : 

 First, the divergence from the median line of the dental arches as 

 they are traced from before backward ; this is much greater in man 

 than it is in the lower animals. Out of 96 examples of dental 

 arches examined by rae 58 were found to be deflected more on the 

 left than on the right (see figs. 3, 4, 5, 6, 9,), 21 deflected more on 

 the right than the left, (see figs. 1, 2) while 17 only were symmetrical. 

 If, as I have assumed, the folds in part at least are the result of compres- 

 sion it follows that abrupt and varying deviations of the boundaries 

 of the palate must greatly disturb the harmonious development of 

 its rugse. 



The deviations of the curves of the vault especially when inter- 

 rupted by a disposition to hyperostosis must also be a disturbing 

 influence. In 90 examples of palates the hyperostosis itself was 

 found in 51. This is certainly a remarkably high proportion and 

 when it is remembered that the specimens were from the mouths of 

 patients who were suffering from chronic nasal catarrh, the associa- 

 tion is suggestive of a relation between coincident causes. 



■'"mi 



Figure 5. 

 The arch is wide. The raphe hes on a conspicuous ridge which 

 forms a hyperostosis. The rugte are irregular, while some in advance 

 are long and entire, others are converted into clusters of. coarse 

 papillce. 



Again, in 90 examinations the sides of the vaults along the range 

 of the bicuspids and molars was in 27 instances, both right and left, 



