CHAPTER XIY, 



THE CAUDAL VERTEBRAE OF ICHTHYORNIS. 

 (Plates XXVIII and XXXIV.) 



The tail in IcMJiyornis is notable mainly for being of the modern 

 ornithic type, thus widely differing from that of both ArcJiceopteryx and 

 Sesperornis, the only other two Mesozoic birds in which this organ is pre- 

 served. The tail in the genus IcMJiyornis was comparatively short, and 

 the terminal vertebrae were coossified. 



A series of seven caudal vertebrae are preserved in one specimen of 

 IcMJiyornis victor (number 1732), and are figured on plate XXVIII. They 

 pertain to the median and distal part of the tail, although not including 

 the extreme end, a portion of the pygostyle, or the part formed by the 

 united centra of the terminal vertebrae, being lost. 



Of the vertebrae preserved in this specimen, the first, probably from 

 the middle region of the tail, has in front a slightly concave articular 

 surface, transversely oval in outline, with the upper margin nearly 

 straight. Back of the articular face, the centrum is moderately constricted 

 below, to expand again for the posterior face, but at the sides the centrum 

 expands immediately to form the transverse processes. The latter are 

 directed nearly horizontally outward and backward, and only slightly 

 downward. They are as broad at base as the side of the centrum, but 

 are both crushed and broken, a short distance from their origin. 



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