THE STRUCTURE AND GROWTH OF THE INCISOR 
TEETH OF THE ALBINO RAT 
WILLIAM H. F. ADDISON AND J. L. APPLETON, JR. 
From the Anatomical Laboratory of the University of Pennsylvania and The Wistar 
Institute of Anatomy, Philadelphia 
TWENTY-NINE FIGURES 
CONTENTS 
LUTE OCCT, Sots Sc ese, ated Gs eee na or em RNs ee dGP eC Oye 43 
JISROTEO A! SUPE? 5 As SOk Seas lhe de touse eee a eer ner Pe EOE Ac UE) oe Se 44 
Materielman cennne (MOOS reer tert ns occ cls ds Sisis via Se 0ee kh wns 2 oe ee ete 46 
PTET OE OMNG ATTA 52 = FS ase ew le 4 vice vos we be oe oe ome eee ale aereenss OMEN 46 
MimTferdescuipilonsoluhe IMCISOnS:......4.-+.. 0 s0- +e oe ete ose eee nee 52 
Microscopic. structureor enamel and dentine........... 0.002. s0..0e+-ven deed 5d 
ewe a pine muna he INGISOLS 9.5 oe os 5c noes is oes gs oe + BE oe eo) SOE 59 
Detailed description of development up to time of eruption................. 61 
JE PUTS URUD) aT CHE "LrLOV ENS Hers 11M trl ee eR 8 Pn Aa nS 7 
Simneecnnrapex Ol TOObM OY USEL 2. {0.05.06 0 bose aoa bes 24s aden So ee 81 
Description of mature tooth and tooth-forming organs, in 5-month animal.. 83 
RarerOMorowuhrotsInelsor Geeta. apace. coc. O: 4a esis. oe nea. en ee 88 
Pe ROR Nir OL SHACISOTMEE UIs tae 8.3% le. aceelascic s wave sed )S aa, te 0 Wend Pee Oe ee 89 
WSS CINTA DT eae env NE Bars Ss yeah esate ecb oY baud o.a aS Shes co RRA SS ASR RO 91 
VASE Te euteUM CMC Ibe CMS sip ie cts, cic oSnsen 4, ciGngnsl-s aye e acct stes Re opera om ee 95 
INTRODUCTION 
The incisor teeth of the Rodentia have long been regarded 
by the zoologist as having a high value for the understand- 
ing of many of the characteristics of this order. For instance, 
in 1888, Cope wrote “nearly all the peculiarities of the rodent 
dental system and manner of mastication are the mechanical 
consequences of an increase in length of the incisor teeth.” 
Tullberg (9899) gives the taxonomic position of the genus Mus, 
proceeding from the more general to the more specific group- 
ing: Rodentia, Simplicidentati, Sciurognathi, Myomorphi, My- 
oidei, Muriformes, Myodontes, Muridae, Murini, Mus. <A 
consideration of these terms merely from an etymological view 
suggests the importance of the teeth and jaws in the classifi- 
43 
JOURNAL OF MORPHOLOGY, VOL. 26, NO. 1 
