THE SUPERIOR MAXILLA. 



203 



Stenson's canal. The suture is rarely seen above and never in front, being concealed 

 by the plate forming the front of the bone. Albrecht ' asserts that each intermaxil- 

 lary is double. In support of this is the fact that in cleft palate the fissure does 

 not always come between the incisor teeth and the canine, but an incisor may be 

 found on its outer side. In reply to this it has been pointed out that three incisors 

 on each side occasionally occur, and that, as anomalies are likely to be found in 

 groups, this is merely an irregular arrangement. Moreover, in cases in which the 

 cleft has but one incisor on each side of it, it is well argued that the original position 

 of the tooth-sacs has no certain relation to the bones (Th. KoUiker^). In sup- 

 port of Albrecht is the occasional presence of a line subdividing the lower surface 

 of the premaxilla ; but, on the other hand, it is not certain that this is really a 

 suture, and there seems no evidence that the premaxilla has two centres of ossifi- 

 cation. While there is much that is plausible in Albrecht' s views, they cannot be 

 considered as established. 



Sir William Turner^ thus concludes an excellent discussion of the question : 

 " What is yet wanted, however, to give completeness to the evidence of the division 

 of the intermaxillary bone into an inner and an outer part is the discovery that the 

 intermaxillary bone normally rises from two distinct centres of ossification, one for 

 the inner, the other for the outer part. Of this we have at present no evidence. 



Fig. 226. 



Alveolar 



Fig. 257. 



Lachrymal groove 



Premaxillary 

 fissure 



Inferior surface of upper jaw at about birth. 



B*^^ Antrum 



Ant. palatine canal Palatal process 



Mesial surface of upper jaw at about birth. 



But, in connection with this matter, we ought not to forget that it is quite recently 

 that the embryological evidence of the origin of the intermaxillary part of the human 

 upper jaw from a centre distinct from that of the superior maxilla has been completed. 

 And yet for nearly a century, on such minor evidence as was advanced by Goethe, 

 — viz., the suture on the hard palate extending through to the nasal surface, — 

 anatomists have believed and taught that the human upper jaw represented both the 

 superior and intermaxillary bones in any other mammal. Where a question in 

 human embryology hinges upon an examination of parts in a very early stage of 

 development, we often have to wait for many years before an appropriate specimen 

 falls into the hands of a competent observer. " 



The upper and lower sides of the bone are at first very near together. The 

 tooth-sacs are directly below the orbit. In the latter part of foetal life the antrum 

 appears as a slight pouch growing in from the nasal side. As the bone grows, the 

 antrum remains for some time on the inner side of the infra-orbital canal. The outer 

 part of the bone, especially towards the malar, is filled with diploe, which subse- 

 quently is absorbed as the sinus extends outward. By the end of the second year 

 the cavity has extended above the first permanent molar ; by the twelfth or thirteenth 

 year, when the second molar has appeared, the antrum approaches, though it has 

 not yet reached, its definite shape. During the first dentition it is separated by the 

 uncut teeth from the front of the bone. 



* Sur les quatres os intermaxillaires, See. d'Antropol. de Bruxelles, 1S83. Die morpho- 

 logische Bedeutung der Kiefer-, Lippen-, und Gesichtsspalten, Langenbeck's Archiv, Bd. xxi. 



^ Ueber das Os intermaxillare des Menschen. Nova Acta der Leopold. Carol. Akad. der 

 Naturforschen, Bd. xliii., 1882. 



* lournal of Anatomy and Physiology, vol. xix., 1895. 



