THE SKELETON OF THE TURTLE. THE UPPER JAW. 229 



The only bone developed in connection with the nasal 

 capsules is the vomer (fig. 39, 19), an unpaired bone lying 

 ventral to the mesethmoid cartilage, and in contact laterally 

 with the maxillae, premaxillae and palatines. 



3. THE UPPER JAW AND SUSPENSORIAL APPARATUS. 



A number of pairs of bones are developed in connection 

 with the upper jaw and suspensorial apparatus, one pair, the 

 quadrates, being cartilage bones, while the rest are all mem- 

 brane bones. 



The squamosals (fig. 38, 2) are large bones which, lying 

 external to the auditory bones, extend dorsal wards 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 (tig. 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 ver- 

 tically-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 post-frontal. 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. 



