108 E. RAMSAY WRIGHT ON THE SKULL AND AUDITORY 



structural peculiarities attributed to the geuus by even hesitating to associate it with the 

 order. Finally, Gill (loc. cit. p. 18) reserves for the geuus one of his eleven families of Nema- 

 tognathi. 



The object of the present paper is to show that Hypophthalmus possesses an air- 

 bladder connected with the auditory organ by intervention of a Weberian apparatus, 

 formed of parts of the anterior vertebrœ modified after precisely the same plan as in the 

 other Siluroids ; but that the apparatus in question and the air-bladder exhibit an extreme 

 reduction recalling that in the genera, Loricaria and Hypostomus. To the late Dr. Sagemehl 

 (No. 6) belongs the credit of insisting tipon the view that the presence of a Weberian 

 apparatus implies community of descent ; as he observes, it is c[uite impossible to conceive 

 of so elaborate a mechanism having been developed independently within the group of 

 the Physostomi more than once. I have elsewhere indicated (No. 11) that Baudelot was 

 the first to give correct homologies for the osseous structures involved in the Weberian 

 apparatus of the Cypriuoids, and to assert that in the Siluroids it is constructed on the 

 same type. The full demonstration of this was furnished by myself in regard to the 

 genus Amiurus. In extending to the Characinidœ and Grymuotidte the demonstration of 

 the morphological identity of the Weberian apparatus, Sagemehl recalls that by Valen- 

 ciennes it was only considered analogous in the various families, and that even by Joh. 

 Millier the structural differences of the apparatus in the families possessing- it were more 

 emphasized than its morphological identity. There can be no c[uestion of the accuracy of 

 Sagemehl's view, and it may confidently be anticipated that in all the forms of Nematog- 

 nathi, Plectospondyli (Jordan, No. 12, pp. Ill and 882), and G-ymnonoti, an air-bladder 

 will either be found or at any rate a profound modification of the anterior vertebrae, 

 showing that its absence is secondary. Sagemehl proposes to unite under the designa- 

 tion Ostariophysece {offrnpiov, ossicle, qjvGij, air-bladder), those Teleosts which possess a 

 Weberian apparatus. It is certainly convenient to have a classificatory term to indicate 

 the community of descent of the forms so characterized. 



Before proceeding to examine the condition of the parts iu question in Hypophthal- 

 mus it may be convenient to recall that which obtains in Amiurus, where the apparatus is 

 probably as fully developed as in any of the Nematognathi. 



The sacciali of the auditory labyrinths of both sides are connected by a transverse 

 duct, from which there projects backward in the middle line a thin-walled sac or sinus, 

 which is accommodated in a special fossa formed by the basi- and ex-occipitals, known as 

 the "cavum sinus imparis." This cavum lies immediately below the medulla oblongata, 

 where it joins the spinal cord, and is continued backwards into two diverticula (the atria 

 sinus imparis) lined by dura mater, which lie right and left of a median partition on the 

 upper surface of the body of the first vertebra. The lateral walls of the atria are formed 

 by the stapedes, the modified neural arches of the first vertebra. Filling up the gap be- 

 tween each stapes and the exoccipital on each side is an intercalated piece or claustrum. 

 The varying states of distension of the air-bladder affect the stapedes (and, consequently, 

 the auditory labyrinth through the Jluid iu the atria and caAUim sinvis imparis) by means 

 of the altered transverse processes of the third vertebra — the so-called " Mallei" — which 

 posteriorlj»^ are connected with the external tunic of the air-bladder, and anteriorly (indi- 

 rectly) with the stapedes, by intermediate pieces — the incudes — which are the altered 

 neural arches of the second vertebra. The first vertebral centrum is distinct and of con- 



