The _pterygoid_ (figs. 24 and 26, 3) is a large bone, whose anterior limb runs forwards meeting the maxillae and palatine; while its inner limb meets the auditory capsule and parasphenoid, and its outer limb runs backwards and outwards to the angle of the mouth. The _palatine_ is a small transversely-placed bone, which connects the pterygoid with the anterior part of the sphenethmoid. The _squamosal_ (figs. 24 and 26, 4) is a T-shaped bone whose anterior arm is pointed and passes forwards to meet the pterygoid. The posterior upper arm is closely applied to the pro-otic, while the posterior lower arm meets the pterygoid and quadratojugal at the angle of the jaw, and surrounds the narrow cartilaginous bar of the quadrate which goes to join the cranium. The squamosal is probably homologous with the squamosal together with the pre-opercular of Bony Ganoids. The quadrate and squamosal form the =suspensorium= by which the lower jaw is connected with the cranium. The =lower jaw= or =mandible= consists of a pair of cartilaginous rods (=Meckel's cartilages=) in connection with each of which there are developed two membrane bones and one cartilage bone. The cartilage bone is the =mento-meckelian= (fig. 26, A, 14), a very small ossification at the extreme anterior end. The membrane bones are the _angulo-splenial_ and the _dentary_. The _angulo-splenial_ is a strong flat bone which forms the inner and lower part of the mandible for the greater part of its length. Its dorsal surface is produced into a slight =coronoid process=. The _dentary_ (fig. 26, A, 15) is a flat plate which covers the outer surface of the anterior half of the mandible, as far forwards as the mento-meckelian. The lower jaw is devoid of teeth. The part of Meckel's cartilage which in most vertebrates ossifies, forming the articular bone, remains unossified in the Frog. THE HYOID APPARATUS. The =hyoid= of the adult Frog is formed of the modified hyoid and branchial arches of the tadpole. It consists of a broad thin plate of cartilage, the =basilingual plate= (fig. 29, B, 1), drawn out into two pairs of long processes, the =cornua=. The basilingual plate is broader in front than behind, and is formed from the fused ventral ends of the hyoid and branchial arches of the tadpole. The =anterior cornua= (fig. 29, B, 2) form a pair of long slender cartilaginous rods which project from the body of the hyoid at first forwards, then backwards, and finally upwards and somewhat forwards again, to be united to the auditory capsules just below the fenestrae ovales. They are formed from the dorsal portion of the hyoid arch of the tadpole and are homologous with the cerato-hyals of the Dogfish. The =posterior cornua= form a pair of straight bony rods diverging outwards from the posterior end of the basilingual plate. They are formed from the fourth branchial arches of the tadpole, and differ from the rest of the hyoid apparatus in being well ossified.