The oral cirri of Silurold» «iid the ori>;in of the head in Vertehrates. 41 B 



Nius. "The lower jaw, varying to an extraordinary extent in shape, 

 possesses often a special coronoid process". It is indicated in Dipnoi 

 by the shape of the jaw, and the cartilaginous coronoid process can 

 well be seen in sections. 



The Selachii are not known to possess a coronoid process, the 

 lower jaw in these animals being far from primitive. 



It is no part of the present paper to follow out the coronoid 

 l)rocess in the Vertebrates, and indeed complete observations on the 

 relative extent of cartilage and bone are still wanting. 



It may be remembered that the rami of the lower jaw of Teleostei 

 are said to lie some way apart in embryos (Stöhr), but this may 

 have nothing to do with the existence of the space between the mento- 

 meckelian processes in Siluroids. 



The anterolateral piece of the tongue apparatus in Myxinoids 

 corresponds, to a certain extent, with the Meckelian cartilage. From 

 its anterior upper corner a coronoid process proceeds to the coronoid 

 piece and on to the maxillary tentacle , the relations in this respect 

 being essentially the same as in Auchenaspis , where maxillary and 

 coronoid tentacles are fused. The branches of the mandibular nerve 

 run outside it however. No mentomeckelian process is present, or 

 only virtually so, and there is no articulation with the quadrate region. 



A number of muscles belonging to the tentacular system are at- 

 tached to Meckel's cartilage. In Myxinoids the number is consider- 

 able. In Teleostei it is almost equally great, but in Selachii there 

 has been much reduction and simplification. Vetter says of the ad- 

 ductor mandibulae of Teleostei: "This muscular mass is nowhere 

 found in the form of the relatively simple undivided adductor of 

 Selachii or of Chimaera but always split into several portions. The 

 Teleostei thus stand in regard to the jaw muscles much nearer to 

 Myxine than the Selachii. 



Many great authorities have held that the adductor mandibulae 

 is the homologue of the adductores arcuum visceralium and that the 

 jaws represent a visceral arch, yet this view appears to me to be 

 entirely erroneous and to have turned subsequent investigations 

 into a wrong path. In spite of the admirable researches of Jo- 

 hannes MüT>LER, FCrbringer and Vetter, much remains to be 

 done, especially in the way of comparison , since the muscles yield 

 most conclusive evidence of the correctness of the Cirrhostomial 

 theory. 



Ur^\. Jahrb. VIU Abth. i Vlorpli. 27 



