24 



as a punctum fixum. This fact alone seems sufficient to show that 

 the hyomandibular of Teleostei must be sought in the 

 articular portion of the quadrate of Heptanchus, that 

 is, in the part proximal to the skull. 



What is then the so-called hyomandibular of Elasmobranchs ? It 

 appears to me to be the stylohyal. There is a very general 

 attachment of the stylohyal by ligaments not only to the symplectic 

 region but also to the cranium (Gadow) and there is nothing remark- 

 able in the supposition that the stylohyal of Heptanchus has gained 

 an attachment almost entirely to the cranium. Unless this be the 

 case a stylohyal is wanting in Notidanidae. 



The gradual transition from the simple piece of Notidanidae 

 attached to the skull by ligaments, to the enormous Suspensorium of 

 e. g. Raia has been demonstrated in an entirely convincing manner 

 by Gegenbaue. 



The spiracular cartilage of other Elasmobranchs may perhaps be 

 regarded (Huxley) as a rudiment of the large articular process of 

 the quadrate (i. e. true hyomandibular) in Heptanchus. 



Physiologically the supposed hyomandibular of Elasmobranchs 

 does not correspond to the hyomandibular of Teleostei and stur- 

 geons, apart from the fact that it articulates in a totally different 

 place on the skull, because the Levator maxillae superioris muscle 

 [Vetter^)] is attached to the quadrate, not to the Suspensorium of 

 ordinary Elasmobranchs while its homologues, the Protractor hyomandi- 

 bularis of sturgeons, the Levator arcus palatini together with the 

 Dilatator operculi of Teleosteans are attached principally to the true 

 hyomandibular. Nor is there any muscle attached to the Suspensorium 

 in Elasmobranchs corresponding to the Retractor hyomandibularis of 

 sturgeons, the Levator and Adductor operculi of Teleostei. The por- 

 tions of the Constrictor superficialis of Elasmobranchs which may 

 correspond to these muscles enter into no relation with the Suspen- 

 sorium. 



Not much evidence can be gained from the relations of the hyo- 

 mandibular nerve and cartilage for they are variable. The nerve as 

 described by van Wijhe passes in front of the hyomandibular in Poly- 

 pterus, it normally pierces the hyomandibular bone in Teleostei, it 

 passes through a notch behind in Acipenser while in Chimaera it is 



1) Vetter, Kiemen und Kiefermusculatur der Fische, Jen. ZeitBchr., 

 VIII. & XII. Bd. 



