287 



a very doubtful one, the so-called maxillary teeth of the fishes mentioned, 

 and their associated bones, being very probably dermopalatine ones. 

 As there is a well developed and tooth - bearing premaxillary bone in 

 both Lepidosteus and Polypterus, we thus probably have in these fishes 

 a new toothed arch, formed by the premaxillary and dermopalatine 

 teeth, and it is apparently this arch that is found in the Amphibia 

 and still higher vertebrates. 



Maxillary and mandibular breathing valves are apparently very 

 generally found in all those fishes that have a premaxillary bone. In 

 the Elasmobranchii, which have no premaxillary bone, the maxillary 

 breathing valve is possibly, or even probably, represented in a part of 

 the nasal velum. In Acipenser it may be represented in the barbels. 

 In Polypterus bones related to teeth are found developed in what are 

 apparently the homologues of both breathing valves. The maxillary 

 breathing-valve bone, so-developed, forms a second, superficial, bony 

 layer on the roof of the mouth cavity, and it, and the valve itself, 

 seem to foretell the secondary palate of the higher vertebi'ates. 



The internal nostrils, in acquiring their final position in the mouth 

 cavity, must cut the maxillary breathing valve, if it persists in higher 

 animals, into three parts, a median and two lateral ones. The re- 

 tention or greater development of one or the other of these parts 

 would give rise to considerable variation in the bony components of 

 the palate. 



Bibliography. 



1) Allis, Edward Phelps jr., The Anatomy and Development of the 

 Lateral Line System in Amia Calva. Journ. of Morph., Vol. 2, No. 3, 

 April 1899. 



2) — — , The Cranial Muscles, and Cranial and Eirst Spinal Nerves 

 in Amia Calva. Journ. of Morphol., Vol. 12, No. 3, March 1897. 



3) — — , On the Morphology of Certain of the Bones of the Cheek 

 and Snout of Amia Calva. Journ. of Morphol., Vol. 14, No. 3, 1898. 



4) — — , The Lateral Sensory Canals of Polypterus bichir. Anat. Anz., 

 Bd. 17, No. 23, 1900. 



5) — — , The Skull, and the Cranial and First Spinal Muscles and 

 Nerves in Scomber scomber. (In press.) 



6) Baur, G„ Ueber die Morphologie des Unterkiefers der Reptilien. 

 Anat. Anz., Bd. 11, No. 13, p. 410—415, Dec. 1895. 



7) Brauer, August, Beiträge zur Kenntnis der Entwickelung und x4.na- 

 tomie der Gymnophionen. II. Die Entwickelung der äußeren Form. 

 Zool. Jahrb., Bd. 12, Heft 3, 22. Febr. 1899. 



8) Bridge, T. W., The Cranial Osteology of Amia Calva. Journ. of 

 Anat. and Physiol., Vol. 11, Part 4, July 1887. 



9) Broom, B,., On the Homology of the Palatine Process of the Mam- 

 malian Premaxillary. Proc. Linn. Soc. N. S. Wales, Ser. 2, Vol. 10. 

 Part 8, 1895. 



