The Skull of Hymenochirus curtipes.

Abstract

Summary.The nasal capsule comprises a small tectum nasi, a septum nasi that is ossified posteriorly, a flat cartilago alaris and a long slender cartilago obliqua. The crista intermedia and its laminae are absent.The nasal cavities consist of three chambers which have been termed the cavum principale, the intermediate chamber and the recessus lateralis. Communicating with the latter is the organ of Jacobson, into the floor of which Jacobson's gland opens. There is no ductus nasolacrimalis or glandula intermaxillaris.The cranial nerves are discussed in connection with the lateral wall of the neurocranium. It is observed that there is a well‐marked preoptic root, but no distinct pila metoptica, the side wall between the foramen opticum and the foramen prooticum representing a combination of the pila metoptica and the pila antotica. It is considered that a prefacial commissure is present.The skull is strongly ossified. The nasals, the fused frontoparietals, the pterygoids and the parasphenoid are large. A small foramen parietale occurs in the fused fronto‐parietals. The pterygoids do not encircle the median Eustaehian aperture, which in section is seen to penetrate the exoccipitale. The sphenethmoicl region is cartilaginous and unpaired. There is no separate supra‐ethmoid or prevomer. The palatines and quadratojugals are lacking. The quadrate region is anteriorly situated. An ossified processus basalis of the quadrate is recognized. The processus pterygoideus is confluent with neighbouring parts, but the processus oticus forms a lateral cartilaginous wall between the pars media plectri and the middle ear.The musculus levator mandibulae anterior seems to be present, as the whole levator muscle occurs laterally and posteriorly to the ramus mandibularis V. The musculus depressor mandibulae consists of superficial and deep sections. Some of the fibres of the latter originate on the hinder process of the pars media plectri and on the posterior extremity of the ceratohyale.The hyobranchial skeleton consists of two completely separated parts. The copula and the ceratohyale are ossified.The affinities of Hymenochirus are discussed and some neotenie features are pointed out.