AIR-BLADDER m NOTOPTERUS BORNEENSIS. 519 



utricular diverticulum iu the prootic. The membraue which closes 

 «ach auditory fontanelle (a.f.), and is invested externally by the 

 tunica interna of the auditory csecutn of the air-bladder, is almosfc 

 ia contact internally with the outer wall of the utricular diver- 

 ticulum. The semicircular canals have the normal arrangement, 

 both as regards their relations to the utrieulus and to the various 

 periotic bones. It may be mentioned, however, that each 

 supero-lateral cranial fontanelle (c.f.) is almost completely en- 

 ■circled by the three semicircular canals — the horizontal canal in 

 the pterotic {pt.) curving round the lower or outer border, the 

 posterior vertical canal in the epiotic (ep.) and opisthotic (o/».), 

 and the anterior vertical canal in relation with the inner surface 

 of the prootic (pro.), being similarly situated with regard to the 

 anterior and hinder margins respectively ; while the vertically- 

 <lisposed common stem, or sinus utriculi superior, by which the 

 two latter canals join the utrieulus, crosses the fontanelle at a 

 short distance internal to the membrane which closes it. 



Careful examination failed to reveal the existence of any con- 

 nection between the sacculi of opposite sides by means of the 

 supra-cerebral or sub -cerebral union of their endolymphatic ducts, 

 such as has been described by Weber (12) for Silurus glanis, and 

 in the case of other Siluroids by Bridge and Haddou (2) and 

 Kamsay Wright (13), and by Hasse (6) for the Herring (Glupea 

 harengus) ; or of any communication between the two utriculi, 

 similar to the sub-cerebral connection which has been described 

 in the last-mentioned Teleost by Weber (12), and in the Shad 

 (Ohtpea alosa) by Breschet (1). It must be admitted, however, 

 that the single specimen of Sotopterus examined by me was 

 not sufficiently well-preserved to quite justify purely negative 

 conclusions on these points. 



VII. COMPARISOIS" WITH NoTOPTEBUS PalLMII' 



As regards the general structure and relations of the various 

 divisions of the air-bladder, the account above given agrees 

 generally with that of N. Pallasii by Cuvier and Yalenciennes. 

 In certain details, however, there are important discrepancies 

 which may be due either to the existence of structural variations 

 in the two species, or possibly to errors in the description of the 

 £ir-bladder of N. Pallasii. The more important of these differences 

 will now be considered. 



39* 



