I04 A MANUAL OF ANATOMY 



and maxilla proper is indicated by the premaxillary suture on the palatal 

 surface of young bones, which may, though somewhat rarely, persist in adult 

 life. This suture extends outwards and forwards from a point directly behind 

 the lower end of Stensen's canal to the alveolar border between the lateral 

 incisor and canine alveoli. 



The premaxilla of each side forms an independent bone in many animals. 

 It may be developed in two parts from separate centres of ossification — an 

 inner for the portion bearing the central incisor alveolus, and an outer for 

 the portion containing the lateral incisor alveolus, and these two portions may 

 remain separate. The inner portion is known as the endognathion, and the 

 outer portion as the mesognathion, whilst the remainder and greater part of 

 the bone is referred to as the maxilla proper. 



The varieties of alveolar cleft palate are explained by a reference to 

 these conditions of the bone. In mesial clelt palate the two premaxillae 

 (right and left) are separated by a mesial cleft. Lateral cleft palate may 

 occur in two forms — the maxilla proper or excgnathion and the entire 

 premaxilla may fail to unite, and the cleft is situated between them, and 

 invades the alveolar border between the lateral incisor and canine alveoli; or 

 the premaxilla may exist in two parts, inner or endognathion, and outer or 

 mesognathion, and the cleft may be between these two, in which case it 

 invades the alveolar border between the central and lateral incisor alveoli. 

 These conditions may occur on one or both sides. 



In the earlier stages of intra uterine life there is no trace of the antrum, and 

 the alveolar border lies close to the infra-orbital border. In the course of the 

 fourth month, however, the antrum makes its appearance as a shallow depres- 

 sion on the inner aspect of the bone, and, as this increases, it gradually 

 separates the orbital, alveolar, and palatal portions. In the process of 

 development the alveolar border first presents an elongated furrow, called the 

 dental groove, on either side of which a plate grows downwards, forming 

 the labial and lingual plates. The groove is thus converted into a trench with 

 these ramparts on either side. Subsequently these plates are connected by a 

 number of septa, which intersect the trench and break it up into alveoli. At 

 this stage these are only five in number for each bone, and the canine alveolus 

 is the first to be partitioned off. In early life the bone contains the temporary 

 teeth, which are five in number on either side, but in the adult, as stated, it 

 contains eight alveoli for the eight permanent teeth. 



The Malar Bones. 



The malar or cheek-bone is situated between the external 

 angular process of the frontal and zygoma of the temporal on the 

 one hand, and the malar process of the superior maxilla on the 

 other, where it separates the orbit from the temporal fossa. It is 

 quadrilateral, and presents two surfaces, four processes, and four 

 borders. The external surface is convex, and near its centre there 

 is the malar tuberosity. Above this is the malar foramen for the 

 passage of the malar branch of the temporo-malar or orbital 

 nerve, and a branch of the lachrymal artery. The portion of this 

 surface close to the zygomatic process gives origin to the zygo- 

 maticus major, and the lower and anterior part to the zygomaticus 

 minor. The internal surface, which is concave, looks into the 

 temporal fossa above and zygomatic fossa below, and it is overhung 

 superiorly by a curved plate of bone, called the orbital process. 

 Anteriorly it presents a rough, slightly serrated, triangular area 

 for the malar process of the superior maxilla. The orbital process 

 projects backwards and inwards, in a curved manner, from the 



