290 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



by ligament. It is also firmly united by ligament to the upper por- 

 tion of the epihyal. 



8. The Suboperculum, 



As above indicated, is seen in the uppermost branchiostegal ray, 

 which occupies exactly the position of the suboperculum in other 

 Teleosts. 



The large anterior extension of the hyomandibular, whereby the 

 metapterygoid is thrust forwards, is a characteristic feature. On 

 examining a young stage it is seen that this extension is not an 

 ossification originally represented by cartilage, but is a growth for- 

 wards of the perichondral bone, of the hyomandibular cartilage into 

 the membrane lying in front. This appears to have been originally 

 due to the relations of the R. hyoideo- , mandibularis N. facialis, the 

 growth being later on carried still more forwards for the attachment 

 of muscles. This has resulted in the hyomandibular usurping the 

 position of the metapterygoid, and its functions as regards the origin 

 of the muse, adductor mcmdibulee, the longitudinal ridge usually 

 being in the metapterygoid. 



The relations and origin of the opercular bones at onetime aroused 

 much discussion ; some light is apparently thrown upon these points 

 by Amiurus, but, before enunciating any theory, it may be well to 

 state briefly the ideas of earlier authors. 



The earlier writers, such as Geoffroy Saint-Hilaire and Spix, were 

 inclined to consider the opercular bones as comparable to the auditory 

 ossicles of the mammalia. Thus the former terms the preoperculum, 

 the 'tympanal,' the operculum, the ' stapeal,' the suboperculum, 

 the ' malleal,' and the interoperculum, the ' inceal ;' while, accord- 

 ing to Spix, the same bones are respectively, leaving out the subo- 

 perculum, the ' marteau,' the 'enclume,' and the ' e"trier.' Cuvier 1 



denies these relationships, saying " plus on examinera les pieces 



operculaires, plus on se convaincra que ni leurs connexions entre 

 elles et avec les autres os, ni les muscles qui les mettent en mouve- 

 ment, ne presentent le moindre rapport avec les osselets dont il 

 s'agit." Neither deBlainville or Agassiz believed in the auditory 

 theory, the former believing the opercular bones to belong to the 



1 Cuvier et Valenciennes.— Hist. nat. des Poissons. Paris, 1S2S. 



