38 THE FROG 
laginous and bony arches, maxillary and mandibular. A carti- 
laginous and bony framework, the suspensorium, serves to attach 
the jaws to the cranium. ; 
(1) The maxillary arch, or upper jaw, contains the. following 
bones in each lateral half: 
The maxilla, a long thin bone forming the greater part of the 
upper jaw. It bears teeth along its entire length. Anteriorly it 
meets the premaxilla, and posteriorly the quadrato-jugal. De- 
scribe its relation to the nasal. 
The premaxilla meets its fellow of the opposite side in the 
middle line anteriorly. Each bears teeth and gives off from its 
dorsal surface a backwardly directed process which forms part 
of the boundary of the nasal opening. In life the premaxillz are 
movable and when pressed against by the tip of the lower jaw 
they are turned slightly backward, closing the nares. 
The quadrato-jugal is the only cartilage bone of the upper jaw. 
Its anterior end articulates with the posterior end of the maxilla 
and its posterior end articulates with the squamosal. It does 
not bear teeth. 
(2) The suspensorium. The jaws are attached to the cranium 
by means of a suspensory apparatus in which the following bones 
are to be distinguished on each side: 
The tympanic or squamosal, a T-shaped bone forming the 
postero-lateral wall of the skull. The stem of the T unites with 
the quadrato-jugal, and the posterior arm of the cross of the T 
abuts against the lateral wall of the prootic. ; 
The pterygoid, a triradiate bone lying beneath the tympanic. 
What are its relations to other parts of the skull? 
The palatine, a slender transverse bone lying in the roof of the 
mouth, and passing between the maxilla and the anterior end of 
the sphenethmoid. 
The nasals, described above, also serve to some extent to brace 
the maxillae. 
Draw (4) a dorsal view of the skull; also a ventral view, 
excluding the lower jaw and the hyoid apparatus. 
(3) The mandibular arch, or lower jaw. Each half consists 
of a cartilaginous core, Meckel’s cartilage (best seen in a wet 
