23 



has been described by Traquair, van Wijhe and myself ^). The bent 

 hyomandibular articulates with the skull in the pterotic region and 

 the spiracle opens in front of the articulation. The chief function of 

 the hyomandibular is to support the operculum which it does by an 

 opercular knob. In the operculum itself can be found traces of carti- 

 lage (van Wijhe). The stylohyal is attached to the lower end of the 

 hyomandibular. The quadrate is separate from the hyomandibular 

 and is continued as the pterygoid bar to the autopalatine (van Wijhe). 

 There is no difficulty in interpreting the parts but it will be seen 

 that there is a departure from the type of the ordinary Teleostean 

 though on the other hand in the independence of the quadrate and 

 certain other points there is a most curious resemblance to the 

 relation of the cartilages in the earliest stages of Teleostei. 



Acipenseridae. The sturgeons are so well known that it will 

 be necessary only to state my general conclusions. With Spatularia 

 they show the extreme modification of the type of suspension in ordi- 

 nary Teleostei and have no similarity, as will be shown, to Selachii. 

 The hyomandibular nerve runs in a bony notch behind the hyomandi- 

 bular while the spiracle when present opens in front of it. As far 

 as I am aware no cartilages are found in the opercular series. 



Elasmobranchii. The Notidanidae are the forms which throw 

 light on the suspensorial apparatus. As is well known Gegenbaur^) 

 regarded the articulation of the quadrate with the postorbital process 

 in Heptanchus as the primitive articulation. This was disputed by 

 Huxley on the ground that the articular process of the quadrate in 

 Notidanus cinereus developes late in the life of the animal. The 

 latter argument has no weight for on similar reasons one would have 

 to regard the wisdom teeth of man as a new acquisition of the human 

 species. 



Very exact descriptions with figures of the ligamentous attach- 

 ments of the so-called hyomandibular are given by Gegenbaur, Hux- 

 ley and Gadow. 



The spiracle opens behind the articulation with the postorbital 

 region i. e. the pterotic articulation and the hyomandibular nerve does 

 not penetrate the quadrate. 



This quadrato - pterotic articulation of Heptanchus corresponds, 

 topographically, exactly with the articulation of the hyomandibular in 

 Teleostei. The spot is situated in definite relation to the anterior and 

 exterior semicircular canals of the ear and therefore may be treated 



1) Gegenbaük, Kopfskelet der Selachier, S. 186. 



2) Zool. Jahrbücher, Anat. Abt., 1892 (with literature). 



