188 



THE COAL MEASURES AMPHIBIA OF NORTH AMERICA. 



diameter the proportion of i to 3. Both the articular terminal facets are deeply and equally 

 concave; but from the center to the margin the surfaces are convex, and this convexity is 

 greatest near the center. * * * The cavities for the reception of the intervertebral matter 

 begin immediately from the margin, and are considerably deeper than the corresponding 

 parts of the Ichthyosaurus, indicating a greater degree of flexibility in the vertebral column. 

 The margins of the vertebrae are some.what raised, as if they had yielded to a forcible com- 

 pression applied longitudinally ; and hence the lateral surfaces of the centers are concave in 

 an anteroposterior direction. This concavity is greater in the upper half of the vertebra 

 and was undoubtedly more marked originally than at present, since the appearance of the 

 margins indicates considerable abrasion. The non-articular surfaces of the centra are 

 smooth and regular; and the external fibres of the osseous tissue are singularly reticulated. 



FIG. 41. Nova Scotian Amphibia. 



A. Oblique lateral view of vertebrae of Eosaurus acadianus Marsh, a, pits 



for articulation of neuropophyses ; b, rudimentary transverse process on 

 right lateral surface of centrum. 



B. Oblique view of vertebra;, a, pits for articulation of neuropophyses; b, 



rudimentary process on lateral surface. 



C. Posterior view of nearly perfect centrum. 



D. Transverse section of same vertebra, showing deep concavities of articular 



terminal facets. 

 E and F. Microscopic sections near surface, showing lacuna; arranged around 



an Haversian canal. Magnified 200 diameters. 

 (All figures after Marsh. X 0.75.) 



' The neuropophyses are not anchylosed to the centrum, as in the mammalia, nor con- 

 nected to it by sutures, as in the crocodiles ; but their union with the vertebra is indicated by 

 two pits, which served for their articulating surfaces. These depressions are situated on 

 the superior surface of the centrum intermediate between the anterior and posterior mar- 

 gins of the extremities. They are circular in form and sink directly into the body of the ver- 

 tebra; instead of being elongated longitudinally and raised by ridges, as in Ichthyosaurus. 

 The pits are about a line in depth, and in the more perfect of the fossils are not in their origi- 

 nal position. The floor of the spinal canal is narrow, being but 5 lines in breadth. A rudi- 

 mentary transverse process, or exogenous tubercle, is sent off from each lateral surface of 

 the centrum, at points equidistant from the extremities of the vertical diameter. Their 



