STRUCTURE AND GROWTH OF INCISOR TEETH 45 
The histology of the incisor was briefly described by Owen 
(40-45) and more completely studied by J. Tomes (’50). The 
latter found a considerable diversity of arrangement of the 
enamel prisms in the different families of the order, so that in 
many cases he was able correctly to refer a tooth to a particular 
family by a simple inspection of thin sections of its enamel. 
Von Brunn (’87) showed that at eruption the tip of the incisor 
of the albino rat is free from enamel, and Sachse (’94) confirmed 
this on Mus musculus. J. L. Williams (’96), in a comparative 
study of the formation of enamel, gives a number of good illus- 
trations of the structure of the enamel and enamel-organ of the 
rat, prepared from microphotographs. 
Ryder (’78) and Cope (’88), in harmony with their views on 
the “Origin of the Fittest,” described the form and position of 
the rodent incisor as manifestations of a most efficient mechani- 
cal system; and studied the various effects on skull topography, 
necessitated by adaptation to this system. 
The enamel organ of the albino rat was studied by von Brunn 
(87) who described in some detail the differences in structure 
between its functional labial portion and its non-functional 
lingual side. He also described the early continuity of the 
lingual side of the enamel-organ and its later penetration by the 
surrounding connective tissue. Roetter (’89), studying Mus 
musculus, denied von Brunn’s position in regard to the invasion 
of the lingual side of the enamel-organ by connective tissue, 
and Sachse (’94), also using Mus musculus, agreed with Roetter 
and described the continuity of the lingual portion as persisting 
through life. 
The development of the rodent incisor has been studied es- 
pecially by Roetter (89), Sachse (’96) and Meyerheim (’98). 
Burckhardt (’06), in his description of the development of the 
persistently growing rodent incisor in O. Hertwig’s Handbuch 
der Entwickelungslehre has followed chiefly Sachse’s work upon 
Mus musculus. In both Weber (’04) and Hertwig (’06) are 
extensive bibliographies and in these may be found all references 
not fully given in our appended list of literature cited. 
