126 ANNALS NEW YORK ACADEMY OF SCIENCES 



in the specimens, showing that there were large muscles there. These 

 muscles might be called the levator capitis muscles, as they raise the head. 

 From the insertion areas this appears to have been a double muscle, one 

 on each side of the median line. The attachment would be under the 

 dorsal shield, where there is a strong keel that would serve as a good 

 insertion for so important a muscle. The depressor capitis must have 

 arisen on the heavy, inner part of the skull, and the specimens show areas 

 that might well have served for this purpose. There is a large depression 

 at the posterior end of the inner side and a strong ridge along the side of 

 the large paired elements that might have covered the cartilage protecting 

 the brain and might have given a base for the muscles. The insertion of 

 this muscle is problematical. It could hardly be inserted on the plastron, 

 for there it would be in the way of the digestive tract. The only other 

 likely place for the insertion of the depressor capitis muscle would be on 

 the so-called "clavicular element/' as the muscle could not have been 

 attached to any part of the skull itself. 



The problem of the musculature of the mandibles is even more of a 

 puzzle than the musculature of the skull. This mandible has been inter- 

 preted in various ways : as a splenial by Eastman and as some other ele- 

 ments by various writers. Whatever its history has been, it is apparently 

 similar to nothing in the Pisces. If it is a splenial it is utterly unlike 

 the splenial of the dipnoans, for they all show a distinct concavity on the 

 outer side of the splenial for the reception of the Meckelian cartilage; 

 and examination of the specimens in the American Museum of Natural 

 History shows no arthrodiran that has any concavity for the Meckel's 

 cartilage. The splenial of Ceratodus is quite concave on the outer side 

 and is shaped in a peculiar manner at the posterior end where the articu- 

 lation with the quadrate takes place. There is none of this in any of the 

 Arthrodira. If this mandible represents one of the outside bones of the 

 gnathostome mandible, the same difficulty remains, for the dipnoan shows 

 that the outer elements are concave on the inside to make a place for the 

 Meckelian cartilage. Thus the arthrodiran mandible seems to be some- 

 thing quite different. From the texture of the outside of the mandible, 

 it would appear that at least the anterior half has been on the surface, 

 while the depressed, posterior half might have been imbedded in tissue. 

 The shape of the posterior end of the mandible makes it very evident that 

 it is more or less free, as is seen in the free end of the teleost maxilla or 

 operculum, where the free end is always thin and blade-like. From 

 analogy, we might well conclude that the same is true in the Arthrodira. 



In the American Museum of Natural History a new mandible of 

 Dinichthys, which will be fully described by Dr. Hussakof, shows a pecu- 



