[37] THE OSTEOLOGY OF AMIA CALVA. 783 



In the lowly organised Sharks, as, for example, the Notidanides and 

 Acanthias, there exists upon the inferior aspect of the snout, on either 

 side, a single nasal aperture, which is incompletely divided by two 

 processes, the nasal flaps, which spring from its margin, and give rise 

 in this way to a medial and a lateral entrance. 



In the more highly organized Selachians, in the Scyllians, among the 

 sharks, and in many rays, a more or less deep groove is found to extend 

 from the medial entrance to the upper margin of the buccal aperture. 

 This is the well-known naso-labial groove, which also appears in the 

 ontogeny of the higher vertebrates, and for the closure of which the 

 median nasal aperture is furnished with a valve, found on the mar- 

 gin of the upper lip and opening in the direction of the nasal cavity. 

 This latter corresponds to the inner nasal opening of the Dipnoi, Am- 

 phibia, and Amniota. These structures have long since been de- 

 scribed by Gegenbaur, and the question only concerns us with respect 

 to the Teleosteans and Ganoids.^^ According to previous notions — still 

 accepted by Gegenbaur — the two openings of the nasal pit in bony 

 fishes and Ganoids correspond to the imperfectly separated nasal valves 

 of the lowly organized Selachii. Balfour ^^ has placed a different inter- 

 pretation upon this. According to his views in the matter, the pos- 

 terior nasal aperture of the higher fishes are homologous with the inner 

 nasal apertures of air-breathing vertebrates, which by a gradual turn- 

 ing of the axis of the nasal capsule have shifted their position from the 

 upper lip to the superior aspect of the head. 



My observations upon fishes compels me to oppose this view, and 

 adhere to the old opinion. There are two arguments that I must cite 

 which conflict with Balfour's notion : one of comparative anatomy and 

 one of the history of development. In a number of Teleostei, among 

 others, all native Oyprinoids examined by me, I found in the immediate 

 neighborhood of the nasal apertures and in the dermal bridge separat- 

 ing the anterior and posterior aperture, a small cartilage, that remained 

 undescribed up to the present time, and that is strictly homologous 

 with the nasal alar cartilage of the Selachians. This cartilage usually 

 has the form of a figure 8, the two loops surrounding the nasal open- 

 ings and the middle piece lying in the dermal bridge between the aper- 

 tures. It is very intimately connected with the skin, so that it becomes 

 a difi&cult matter to make a dissection simply trusting to the scalpel and 

 forceps, but by the aid of a microscope, and carrying the incisions 

 through the nasal region, one can very easily satisfy himself of its pres- 

 ence. It possesses the characteristics of hyaline cartilage and differs 



*^C. Gegenbaur, Gmndzuge ^er vgl. Anatomie, II Aufl., 1870, pag. 754, und das Kopf- 

 sTcelet der SelacMer, 1872, pag. 97 m216. [C. Gegenbaur, Elements of Comp. Anatomy, 

 II Edit., 1870, page 754, and the skeleton of the Selachian head, 1872, pages 97 and 

 216.] 



*^F. M. Balfour, Manual of Comparative Embryology, 1881, Vol. II, page 477. 



