1. sphenethmoid. 2. fronto-parietal. 3. pterygoid. 4. squamosal. 6. exoccipital. 7. parasphenoid. 8. pro-otic. 9. quadratojugal. 10. maxillae. 11. nasal. 12. premaxillae. 13. anterior nares. 14. vomer. 15. posterior nares. 16. palatine. 18. columella. 19. quadrate. 20. occipital condyle. II. optic foramen. V. VII. foramen for exit of trigeminal and facial nerves. IX. X. foramina for exit of glossopharyngeal and pneumogastric nerves.] The patch of unossified cartilage immediately external to the occipital condyle is pierced by two small foramina, through which the ninth and tenth nerves leave the cranial cavity. The ninth nerve passes through the more external of these foramina, the tenth through the one nearer the condyle. The foramina lie however very close together and are sometimes confluent. The cranial walls for a considerable distance in front of the occipitals are unossified, but the anterior end of the cranial cavity is encircled by another cartilage bone, the =sphenethmoid= (figs. 24 and 25, 1) or girdle bone. This partly corresponds to the orbitosphenoids of the Newt's skull. Anteriorly it is pierced by a pair of small foramina through which the ophthalmic branches of the trigeminal nerve pass out. The anterior part of the cranial cavity is divided into two halves by a vertical plate, the =mesethmoid=. Some little distance behind the sphenethmoid the ventro-lateral walls of the cartilaginous cranium are pierced by a pair of rather prominent holes, the =optic foramina= (figs. 24 and 25, B, II), and at a similar distance further back, occupying a kind of notch in the pro-otic are the large =trigeminal foramina=, through which the fifth and seventh nerves leave the cranium. Between the trigeminal and optic foramina are the very small foramina for the sixth nerves (fig. 25, B, VI). The _membrane bones_ of the cranium proper include the _fronto-parietals_ and the _parasphenoid_. The _fronto-parietals_ (figs. 24 and 26, A, 2) form a pair of long flat bones closely applied to one another in the middle line, the line of junction being the =sagittal suture=. They cover over the fontanelles and overlap the sphenethmoid in front. The _parasphenoid_ (figs. 24 and 26, B, 7) is a bone shaped like a dagger with a very short handle. It lies on the ventral surface of the cranium, the blade being directed forwards and underlying the sphenethmoid; its lateral processes underlie the auditory capsules. (2) THE SENSE CAPSULES. The sense capsules are cartilaginous or bony structures which surround the olfactory and auditory organs and are closely united to the cranium. [Illustration FIG. 25. A DORSAL AND B VENTRAL VIEW OF THE CRANIUM OF A COMMON FROG (_Rana temporaria_) from which the membrane bones have mostly been removed. × 2 (after PARKER).