The _frontals_ are a pair of small bones lying immediately in front of the parietals, and in front of them are the _prefrontals_ (figs. 38 and 39, 20), a pair of similar but still smaller bones, which are produced ventrally to meet the vomer and palatines. They form also the dorsal boundary of the anterior nares. The _postfrontals_ (figs. 38 and 39, 18) are larger bones, united dorsally to the frontals and parietals, posteriorly to the squamosals, and ventrally to the jugals and quadratojugals. All three pairs of frontal bones, especially the postfrontals, take part in the bounding of the orbits. [Illustration FIG. 39. LONGITUDINAL VERTICAL SECTION THROUGH THE CRANIUM OF A GREEN TURTLE (_Chelone midas_). × 2/3. (Camb. Mus.) 1. parietal. 2. squamosal. 3. quadrate. 4. basisphenoid. 5. basi-occipital. 6. quadratojugal. 7. pro-otic. 8. opisthotic. 9. pterygoid. 10. palatine. 11. rod passed into narial passage. 12. exoccipital. 13. epi-otic fused to supra-occipital. 14. supra-occipital. 15. premaxillae. 16. maxillae. 17. jugal. 18. postfrontal. 19. vomer. 20. prefrontal. 21. frontal. V, VII, VIII, IX, X, XI, XII, foramina for the exit of cranial nerves.] 2. THE SENSE CAPSULES. Skeletal structures occur in connection with each of the three special sense organs of hearing, sight, and smell. The =Auditory capsules=. The auditory or periotic capsule of the turtle is rather large and its walls are well ossified, epi-otic, pro-otic and opisthotic bones being present. The =epi-otic= (fig. 39, 13) is the more dorsal of the three bones, and in the adult is completely ankylosed with the supra-occipital. The =opisthotic= (fig. 39, 8) is the ventral posterior element. On its inner side it is united to the supra-occipital above, and to the exoccipital below; it sometimes becomes completely fused with the exoccipital. In front it meets the pro-otic, and on its outer side the squamosal and quadrate. Its anterior portion is hollowed out by the cavity in which the auditory organ lies, it gives off also a process which is separated from the exoccipital by an oval foramen through which the glossopharyngeal, pneumogastric, and spinal accessory nerves leave the cranial cavity. The =pro-otic= is the anterior element; it meets the supra-occipital and opisthotic posteriorly, while anteriorly it is separated from the alisphenoidal plate of the parietal and pterygoid by a large oval foramen through which the maxillary and mandibular branches of the trigeminal nerve pass out (fig. 39, V 1 & 2). It is hollowed out posteriorly by the cavity in which the auditory organ lies, and its inner wall as seen in longitudinal section is pierced by a foramen through which the external carotid artery and facial nerve leave the cranial cavity,--the nerve finally leaving the skull through a small oval foramen on the anterior face of the pro-otic near its junction with the quadrate.