The squamosals (fig. 38, 2) are large bones which, lying external to the auditory bones, extend dorsalwards to meet the parietals and postfrontals, and form a large part of the false roof of the skull. They are united ventrally with the quadrates and quadratojugals.
Each quadrate (fig. 38, 3) forms the outer boundary of the tympanic cavity, and is firmly united on its inner side with the opisthotic, exoccipital, and pterygoid. Dorsally it is fixed to the squamosal and anteriorly to the quadratojugal. Its outer surface is marked by a deep recess, and it ends below in a strong condyle with which the mandible articulates. In front of the quadrates are a pair of thin plate-like bones, the quadratojugals which are united in front to the jugals or malars.
The jugals (fig. 38, 17) are also thin plate-like bones, and form part of the posterior boundary of the orbit. They are attached dorsally to the postfrontals, and anteriorly to the maxillae, while each also sends inwards a horizontal process which meets the pterygoid and palatine.
The maxillae (figs. 38 and 39, 16) are a pair of large vertically-placed bones, each drawn out ventrally into a straight, sharp, cutting edge. They form the lateral boundaries of the anterior nares, and each sends dorsalwards a process which meets the postfrontal. Each also sends inwards a horizontal palatine process, which meets the palatine and vomer, and also forms much of the floor of the narial passage.
The premaxillae (figs. 38 and 39, 15) are a pair of very small bones forming the floor of the anterior narial opening, they are wedged in between the two maxillae, and send back processes which meet the vomer and palatines.
The palatines (fig. 39, 10) are a pair of small bones firmly united with the pterygoids behind, with the maxillae and jugals externally, and with the vomer in the middle line. Each also gives off a palatine plate which unites with the expanded lower edge of the vomer, and forms the ventral boundary of the posterior nares. Anteriorly the palatines form the posterior boundary of a large foramen through which the ophthalmic branches of the fifth and seventh nerves pass to the olfactory organs.
The pterygoids (fig. 39, 9) are a pair of large bones which unite with one another by a long median suture. They are united also with the palatines in front, and with the quadrate, basisphenoid, basi-occipital, and exoccipitals behind. Each also sends dorsalwards a short alisphenoid plate which meets that from the parietal.
Piercing the posterior end of the pterygoid is the prominent opening of the carotid canal; a bristle passed into this hole emerges through a foramen lying between the pro-otic and the alisphenoid process of the pterygoid.
(2) The Lower Jaw or Mandible.
The mandible consists of one unpaired bone, formed by the fusion of the two dentaries, and five pairs of bones, called respectively the articular, angular, supra-angular, splenial and coronoid.