The Teeth 



313 



connective tissue, and, 3, the cementum and dental and alveolar 

 periosteum from the mesoblastic dental follicle. 



Fig. 44. Sagittal section through an inferior grinder of an equine 

 embryo, 4 inches long. ect, ectoderm of mouth cavity ; mes, 

 mesoderm ; eo, enamel organ ; ec, enamel cells ; d, den- 

 tine ; eb, embryonic bone. 



The enamel cap is at most points detached from the dentine 

 papillae. The .section through the tooth follicle is so made that 

 the plicae of the enamel cap have split each of the dentine 

 papillae so that there are four instead of two. 



When the bony jaws form later, the teeth are at first in con- 

 tinuotis grooves, but transverse osseous partitions later extend 

 between the tooth germs and finall}' constitute separate compart- 

 ments, or alveoli, for each. The permanent teeth are developed 

 as outgrowths from the enamel organs of the temporary set in 

 those cases where they are preceded by such ; in the others they 

 are formed the same as the temporary teeth from a backward 

 growth of the common enamel germ. 



The teeth of domestic animals, and especially of the horse, are 

 subject to many aberrations in development. The mesoblastic 

 connective tissue follicle, under disturbances, ma}- undergo seri- 

 ous aberration during its developmental stages. There may be a 



