MORPHOLOGICAL REVISION 



97 



tinct spines above. The two halves are separated in some specimens and 

 united below in others; this seems to be a character of age. The spines are 

 directed backwards at a considerable angle, and lie on either side of the 

 large spine of the second vertebra. This is a common structure in many 

 of the Stegocephalia; it occurs in Trimerorhachis and others. The degree 

 of inclination varies in different specimens and is probably extreme in the 

 specimens figured. On each half of the vertebra there is a small process 

 opposite the neural canal, which probably articulated with the skull or with 

 a rudimentary vertebra, in the position of the proatlas of the reptiles. The 

 posterior zygapophyses are small and articulate, with equally small processes 

 on the second vertebra. There was, without doubt, a large intercentrum 

 between the first and second vertebrae. 



Fig. 28. — Eryops megacephalus. No. 4180 Am. Mus. Y. yi. 



A. Lateral view of the first five vertebrje. 



B. Anterior view of neural arch of first vertebra. 

 Fig. 29. — Eryops megactphalus. No. 4893 Am. Mus. X f . 



Sacral vertebra from left side. 



Fig. 28. 



Fig. 29. 



The faces of the occipital condyles look downward as well as inward, 

 requiring the presence of an exceptionally large intercentrum for the first 

 vertebra; this intercentrum bt^re the main faces for the occipital condyles. 



The second vertebra, the axis, has the neural spine nearly twice as wide, 

 anteroposteriorly, as the normal dorsal vertebra. The anterior edge of the 

 spine is thin, and separates the two halves of the spine of the first vertebra. 

 The posterior zygapophyses are normal in size. The transverse processes 

 stand out prominently from the sides of the neural arch and bear faces for 

 the single-headed rib. The intercentrum is normal, but does not bear a 

 facet on the posterior edge for the lower part of the rib head. 



The third vertebra is normal. 



The fourth vertebra resembles the others in all respects but the neural 

 spine; this is only one-half the size of those before and behind it. The upper 

 end seems to fit into a notch formed by the overhanging anterior edge of the 

 fifth. This peculiar character is observable in three specimens (see fig. 28 a). 



From the fifth to the eighteenth, the vertebrae are very similar in form. 

 The neural spines are slender, with somewhat expanded and rugose apices, 

 which lie nearly in a straight line. The dorsal vertebrae of Eryops have been 



