supports the eyeball), found inside the orbit, was circular in shape and formed by consecutive bony plates. The snout was formed by the , r, r and bones. The nasal was generally rounded but some individuals had a sharp nasal boss (a feature that has been called "nasal horn"). In P. hellenikorhinus this boss was divided in two sharp and long ridges. The maxilla was very deep and had up to 15 alveoli (tooth sockets) on its underside or teeth bearing surface. The premaxilla had two alveoli on its lower edge—a character that was present at least on P. andrewsi. The rostral bone was devoid of teeth, high and triangular in shape. It had a sharp end and rough texture, which reflects that a rhamphotheca (horny beak) was present. As a whole, the skull had four pairs of fenestrae (skull openings). The foremost hole, the nares (nostril opening), was oval-shaped and considerably smaller than the nostrils seen in ceratopsids. Protoceratops had large orbits, which measured around in diameter and had irregular shapes depending on the individual. The forward facing and closely located orbits combined with a narrow snout, gave Protoceratops a well-developed binocular vision. Behind the eye was a slightly smaller fenestra known as the infratemporal fenestra, formed by the curves of the jugal and squamosal. The last openings of the skull were two parietal fenestrae (holes in the frill). The lower jaw of Protoceratops was a large element composed of the , , , and . The predentary (frontmost bone) was very pointed and elongated, having a V-shaped symphyseal (bone union) region at the front. The dentary (teeth-bearing bone) was robust, deep, slightly recurved, and fused to the angular and surangular. A large and thick ridge ran along the lateral surface of the dentary that connected the coronoid process—a bony projection that extends upwards from the upper surface of the lower jaw behind the tooth row—and surangular. It bore up to 12-14 alveoli on its top margin. Both predentary and dentary had a series of foramina (small pits), the latter mostly on its anterior end. The coronoid (highest point of the lower jaw) was blunt-shaped and touched by the coronoid process of the dentary, being obscured by the jugal. The surangular was near triangular in shape and in old individuals it was coossified together with the coronoid process. The angular was located below the two latter bones and behind