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_. The fused _dentaries_ (fig. 38, 12) form by far the largest of the bones; they constitute the flattened anterior part of the mandible, and extend back below the other bones almost to the end of the jaw.