THE BONES OF THE SKULL. 153 
it is separated by the diastema, in which no teeth occur, from a 
corresponding but imperfectly differentiated process of the pre- 
maxilla. 
The palatine process (processus palatinus) extends toward 
the median plane. It forms with its fellow of the opposite side 
about two-thirds of the palatine bridge. 
The orbital process (processus orbitalis) is directed obliquely 
toward the dorsal surface of the skull. In conjunction with the 
lacrimal bone and the maxillary process of the frontal, it forms the 
anterior orbital rim. It is continuous with the fenestrated portion 
of the body, and its appearance as a process is largely due to its 
solid character as compared with the perforated surface lying in 
front of it. 
The zygomatic process (processus zygomaticus) forms the 
anterior root of the zygomatic arch, and in the adult condition 
has fused with it the anterior end of the zygomatic bone. Its 
ventral angle bears a prominent masseteric spine for the attach- 
ment of the ligament of the masseter muscle. 
The sphenoorbital process (processus sphenoorbitalis) lies 
on the medial wall of the orbit, in a position opposite to the middle 
portion of the ridge lodging the posterior cheek-teeth. It forms a 
stout buttress, the tip of which is applied to the anteroventral 
angle of the frontal bone. In this position it is visible from the 
orbit, lying between the lacrimal bone and the ethmoidal process 
of the orbitosphenoid. 
13. THE PREMAXILLA. 
The premaxilla, or incisive bone (os incisivum), forms the 
anterior portion of the upper jaw. It comprises a central portion, 
the body—including with the latter the scarcely differentiated 
alveolar portion containing the large and small incisors—a 
frontal process, and a palatine process. The body forms a 
portion of the palatal surface of the skull and of the lateral boun- 
dary of the incisive foramen. Its dorsal surface forms part of the 
boundary of the piriform aperture, the remaining portion of this 
