36 H. B. POLLARD. 



and to judge from the appearance of the cartilage there has been no 

 resorption, so that probably it never extended further at earlier stages 

 of its ontogeny. The mentomeckelian processes are as far from reach- 

 ing the symphysis as in Trichomyctfirus. 



In Auclienaspis the condition is a little different from that of 

 Trichornycterus. The posterior arm is in the same state and the 

 processus coronoideus passes up, and bears the coronoid piece. The 

 mentomeckelian process is, however, longer, reaching halfway from the 

 coronoid process to the symphysis, tapering away. 



In Silurus, where the cartilage is more extensively present, the pos- 

 terior arm extends beyond the articulation with the quadrate, as an 

 angular process, and the mentomeckelian process is fused with its fellow 

 and the symphysis. In Hi/postomidae the whole rami of the lower jaw 

 may be said to be free, there being no symphysis. A processus 

 coronoideus is stated to be frequently present in fish by Stannius. 

 " 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 process 

 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 (Stohr), 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 corres- 

 ponds, 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 

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



