. The science and practice of dental surgery. eg-ment and the absence of tooth formation in the mesognathion segment (see Fig. 15), sotltat the supernumerary tooth is mistaken forthe lateral incisor and the cleft is consequentlystated to pass between the lateral incisor andcanine. Now if in additionto the supernumerary tootha lateral incisor is formed inthe lateral nasal process, thelatter tooth is then ingeni-ously called a pre-canine, toavoid designating both teethas lateral incisors. In otherwords, it is the developmentof the teeth that is subjectto variation and rarely theposition of the c
. The science and practice of dental surgery. eg-ment and the absence of tooth formation in the mesognathion segment (see Fig. 15), sotltat the supernumerary tooth is mistaken forthe lateral incisor and the cleft is consequentlystated to pass between the lateral incisor andcanine. Now if in additionto the supernumerary tootha lateral incisor is formed inthe lateral nasal process, thelatter tooth is then ingeni-ously called a pre-canine, toavoid designating both teethas lateral incisors. In otherwords, it is the developmentof the teeth that is subjectto variation and rarely theposition of the cleft, so thatwhen the teeth are normallydeveloped the alveolar cleftpasses between the centraland lateral incisors. A simple or incompletehare-lip results from failureof union of the naso-frontaland maxillary processes. Ifthis failure of union extendsto the lateral nasal process,the cleft will then involve the alveolus andopen into the nostril—a condition known as analveolar or complete hare-lip and usually asso-ciated with a cleft ?!/. Fio. 7.—Transverse section of a sheep-embryo between the second and thirdweeks (after Bonnet).Medullary or primitive groove; m. Mesoderm; h. Entoderm; mesoderm; vm. Visceral mesoderm; pe. Primitive endocardium ;hp. Heart plates; ppc, Pleuro-pericardial cavity; pp. Pericardialplates; c, Coelom; am. Amnion. The Notochord is formed from tlieentoderm in the region of the medullary groove. Coalescence of the palatine portions of the naso-frontal, lateral nasal, and maxillary processescommences at the anterior palatine foramen andextends both forwards and backwards from this point, the lip and tlie uvnla being the last partsto unite; so that a cleft lip or cleft uvula mayexist without the involvement of the jaw,whereas the reverse condition would be im-possible for developmental reasons. Failure of union of the naso-frontal and lateralnasal processes medially \\ith the maxillaryprocess laterally gives rise to what is known asa
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectdentistry, bookyear19
