+-------------------------+------+ | Pineal Nerve. | | +-------------------------+ | | II | Si. | +-------------------------+ | | I | | +-------------------------+------+ | Vertebrate. | | +-------------+-----------+------+ | Coelomic |V. Wijhe's | | | Cavities. | Segments. | | | | | | +-------------+-----------+ | | Anterior. | ... | | +-------------+-----------+ | | Premandi- | | | | bular | | | | Ventral | | | | part forms | 1 | | | pituitary | | | | body. | | | | pituitary | | | +-------------+-----------+ | | Mandibular |} | Ii. | | |} | | +-------------+} 2 | | | Mandibular |} | | | |} | | +-------------+-----------+ | | Hyoid_1 | 3 | | +-------------+-----------+ | | Hyoid_2 | 4 | | | | | | +-------------+-----------+ | |2nd Branchial| 5 | | +-------------+-----------+------+ {324}SUMMARY. The general consideration of the evidence of the number of segments, and their nature in the pro-otic region of the vertebrate, as given in the last chapter, is not incompatible with the view that the trigeminal nerve originally supplied seven appendages, which appendages did not carry branchiæ, but were originally used for purposes of locomotion as well as of mastication. Such appendages clearly no longer exist in the higher vertebrates, the muscles of mastication only remaining; but in the earliest fish-forms they must have existed, as, indeed, is seen in Pterichthys and Bothriolepis. Judging from all the previous evidence some signs of their existence may reasonably be expected still to remain in Ammocoetes. Such is indeed the case.