The anterior end of the skull is formed by a pair of rather small bones, the _premaxillaries_, which carry the incisor teeth; they bound the sides of the nasal opening, or _anterior nares_, reaching to the nasals, when the latter are of ordinary length; they also form the front end of the hard or bony palate, which divides the nasal passage from the mouth. The _maxillaries_, or upper jaw-bones, make up nearly all of the facial region on each side and send inward to the median line from each side a bony plate which together constitute the greater part of the hard palate; the remainder of the upper teeth are implanted in the maxillaries. A varying proportion of the hinder part of the hard palate is formed by the _palatines_, which also enclose the _posterior nares_, the opening by which the nasal passage enters the back part of the mouth. The maxillary of each side extends back to the orbit, which it bounds anteriorly and in the antero-superior border of which is the usually small _lachrymal_. The inferior, and more or less of the anterior, border of the orbit is made by the cheek-bone (_malar_ or _jugal_) which may or may not have a postorbital process extending up toward that of the frontal; when the two processes meet, the orbit is completely encircled by bone, but only in monkeys, apes and Man is there a bony plate given off from the inner side of the postorbital processes, which extends to the cranial wall and converts the orbit into a funnel-shaped cavity. For most of its length, the jugal projects freely outward from the side of the skull and extends posteriorly beneath a similar bar of bone, the _zygomatic process_ of the _squamosal_. This process and the jugal together constitute the _zygomatic arch_, which on each side of the skull stands out more or less boldly, and the size and thickness of which are subject to great variation in different mammals, the massiveness of the arch being proportional to the power of the jaws. One of the principal muscles of mastication (the _masseter_) is attached to the zygomatic arch.