The Structure of Dinichthys 



195 



neurocranium. Beginning at the front, we find the first clear traces of the neurocranium 

 in the olfactory capsules. These structures, which Newberry described (1889) as eye 

 capsules, can, according to the investigations of Stetson (1930), only be regarded as nasal 

 capsules. Their structure reminds us very much of the nasal capsules of modern Elasmo- 

 branchs. We can say, with certainty, that they were placed not far back of the nasal 



Text-figure 84. 



A schematic drawing of the head of Dinichthys from below, showing the neurocranium 



(shaded in parallel lines) and the gnathal muscles (lined and numbered). 



E, eyeball; /m, foramen magnum; ^c, nasal capsule; no, nervus opticus; ?ip, neurocranial process; oc, 

 otic capsule (?); P, pineal organ; to, tractus olfactorius; f and 11, gnathal muscles. 



Openings (Text-figures 83 and 84 NC). These nasal capsules formed the front part of the 

 neurocranium. 



The next parts which without doubt bordered the neurocranium were the neuro- 

 cranial processes (Text-figures 13, 83 and 84 Np)- A section through this part of the head 

 roof (Text-figure 38 B) shows clearly a well defined cavity, broadest at the top, narrower 

 at the bottom. These two processes have usually been regarded as muscle attachments 

 (Adams 1919, Woodward, 1922, Stetson 1930). Claypole (1892.2) described them as 



