The Structure of Dimchthys 189 



"musculi levatores capitis" (Text-figures 76, LC; 79-81, 83 and 84 I) were attached on 

 one side to MB on the head roof, on the other side to the keel on MD. The strongly- 

 thickened hind part of the head root (MB) (Text-figures 13 and 16b), with its rough 

 surface and with deep impressions and ridges, shows clearly that the musculi levatores 

 capitis were very strong. The deep double impression (ds) on MB serves as a more solid 



Text-figure 80. 

 The author's reconstruction of the armor of Dinichthys to show the mouth mechanism — the mouth open. 



/, musculus levator capitis; I/, musculus depressor capitis; IJ!, musculus levator gnathalis; IV, musculus depressor gnathalis. 



attachment for these muscles. The other ends of the musculi levatores capitis were 

 attached to the underside of MD and especially to its strongly developed keel. Doubtless, 

 the thickened hind edges of the keel served as the chief attachment place for muscle liga- 

 ments. 



Adams fastened the hind ends of these muscles not far from the hind margin of MD. 

 In my opinion this is wrong. This part of MD shows no traces of muscle attachments, 

 and such a heavy muscle as the levator capitis would leave a distinct trace on the surface 

 of the bone. 



The development of more or less strong keels on different parts of the skeleton, as 

 attachments for muscles, is a commonly known fact. Here, we shall only point out two 

 examples which remind us of the arrangement in Dinichthys. In all carinate birds the 

 strongly developed keel (carina) on the sternum is very like the keel in Dinichthys. Also it 

 is here that the well developed and very important flying muscles are attached. Another 

 example shows closer analogy with Dinichthys. If we study the head structure of the 

 fossil saber-toothed tiger, Smilodon, we can easily see traces of the attachment of very 

 strong muscles at the back of the head. On the second or axis vertebra, we find an un- 



