THE MALAR BONES. 131 
between them. They first make their appearance in the second month of intrauterine 
life, shortly after the clavicle has begun to ossify. By the sixth month they are so united 
that their independent character is obscured. Five centres are described—an external or 
malar, which forms the bone to the outer side of the infra-orbital canal; an ¢nner or 
orbito-nasal, from which is developed the inner part of the floor of the orbit, the frontal 
process, and the wall of the antrum; a palatine, for the posterior three-fourths of the 
palatal process ; a nasal, situated between the frontal process and the canine tooth ; and 
within this and nearer the middle line and below, an inczsive centre, from which the pre- 
maxillee are developed, thus forming the anterior fourth of the palatal process in the 
adult. In the early stages of the development of the bone the alveolar groove, in which 
the teeth are developed, lies close below the infraorbital groove, and it is not till later 
that they become separated by the growth of the 
antrum, which first makes its appearance as a shallow 
fossa to the inner side of the orbito-nasal element about 
the fourth month. In the adult bone the course of the 
infraorbital canal and foramen serves to indicate the 
line of fusion of the orbito-nasal and malar elements, 
whilst the position of the anterior palatine canal serves 
to determine the line of union of the incisive with the 
palatal elements. In addition to the foregoing centres, 
Rambaud and Renault describe another w hich, together 
with its fellow, is wedged in between the incisive and 
the palatal elements beneath the vomer, thus explaining 
the Y-shaped arrangement of the foramina of Stenson, 
which open into the anterior palatine canal. 
The premaxille, which in most vertebrates are in- 
dependent bones lying in front of the superior maxillee, 
constitute in man and apes the portions of the upper 
jaw which lie in front of the anterior palatine foramen, 
and support the superior incisor teeth. They are 
developed from the incisive centres above described ; 
the line of fusion of these elements with the maxillee 
proper can readily be seen in young skulls, and occa- 
sionally also in the adult. It corresponds to a suture 
which passes on the palate obliquely outwards and 
forwards, from the anterior palatine foramen to the yg 199, OssrrrcaTton or SUPERIOR 
interval between the lateral incisor and the canine MAXILLA. 
tooth. In cases of alveolar cleft palate the adjacent A, Outer side; B, Inner side; C, 
bones fail to unite along the line of the suture. In Under side. a, Nasal process ; 0, 
some instances, however, the cleft passes outwards Orbital plate; ¢, Anterior nasal 
between the central and lateral incisor teeth, and this  7'*> hae ies ec Ceon s 
’ Infraorbital foramen; (f, Anterior 
condition suggests the explanation that the premaxillary palatine groove ; g, Palatal process ; 
element is denied from two centres—a lateral and a /#, Premaxillary suture; 7, Alveolar 
mesial. The researches of Albrect and Warinski have — Process. 
confirmed this view. The latter anatomist further observes that the lateral cleavage may 
lead to a division of the dental germ of the lateral incisor tooth, and so explain the 
occurrence of the supernumerary incisor which is occasionally met with. In this way the 
different varieties of cleft palate are readily explained ; mesial cleft palate being due to 
failure of union between the two premaxillary bones. Lateral cleft palate may be of two 
types: the cleft in one case passing forward between the central and lateral incisor, and 
being due to the non-union of the two elements from which the premaxilla is primarily 
developed ; the other, in which the cleft passes between the lateral incisor and the 
canine, or between the lateral incisor and a supernumerary incisor, owing to the imperfect 
fusion of the premaxilla laterally with the maxilla. 
THE MALAR BONES. 
The malar bone (os zygomaticum) underlies the most prominent part of the 
cheek, and is hence often called the cheek-bone. Placed to the outer side of the 
orbital cavity, it forms the sharp external border of that hollow, and serves to 
separate that space from the temporal and zygomatic fosse which le behind; 
below, it rests upon and is united to the superior maxilla; behind, it enters into 
the formation of the zygomatic arch which bridges across the temporal fossa. 
9a 
