57 



Nun hat aber schon vor Jahren A. v. Koelliker in seinen Vor- 

 lesungen über Entwickelungsgeschichte (1861) als Stütze für jene 

 Lehre „die freilich seltenen Fälle von Aorten" herbeigezogen, „die in 

 ihrer ganzen Länge durch eine Scheidewand geteilt sind" und für 

 das Kaninchen und Hühnchen hat TtJRSTiG^) sogar die Vorstufe 

 der beiden primitiven Aorten in Gestalt von ursprünglich gesonderten, 

 von der Peripherie gegen die Mittellinie zu vorwachsenden Gefäß- 

 sprossen nachgewiesen. 



Nachdruck verboten. 



The Existence of Skeletal Elements between the Mandibular and 

 Hyoid Arches in Hexanchus and Laemargus. 



By Philip J. White, M. B. 



Professor of Zoology, university College of North Wales, Bangor. 



With 3 Figures. 



Recently two specimens of the six-gilled shark Hexanchus 

 g r i s e u s came into my possession and I took the opportunity of 

 studying their visceral skeletons and of contrasting them with the 

 description given by Gegenbaur -) of these parts in this species. 

 I was naturally curious to do this as my observations on the lower 

 portion of the visceral skeleton in the Greenland Shark ^) had led me, 

 on account of the variations I met with there, to think that variations 

 would most likely occur in such a primitive form as Hexanchus. I 

 have never regarded Gegenbaur's representation of these parts in 

 Hexanchus as altogether expressing the typical arrangement for that 

 species, but simply as one of several possible modifications *). 



However, the object of my remarks at present is to draw attention 

 to the existence of skeletal elements between the mandibular and 

 hyoid arches in the two specimens of Hexanchus before me. In 

 each of these I find a series of cartilages (Fig. 1 and 2 A) lying 



1) Citirt nach Schwalbe's Jahresbericht, Jahrgang 1884 und 1886. 



2) Gegenbaüe, Untersuchungen zur vergleichenden Anatomie der 

 Wirbeltiere. — Das Kopfskelet der Selachier, als Grundlage zur Beurtei- 

 lung der Genese des Kopfskeletes der Wirbeltiere. 



3) White, On the Skull and Visceral Skeleton of the Greenland Shark 

 Lsemargus microceph alu s. Anat. Anz., 1890, p. 259, and Trans. 

 Roy. Soc. Edin., Vol. 37, 1892, Part 2, No. 15. 



4) I intend later to publish the results of my work with regard to 

 the variations which occur in Laemargus. 



