CHAPTER XIII. 



PELVIC ARCH OF ICHTHYORNIS AND APATORXIS. 

 (Plates XXII, XXVIII, and XXXII.) 



The pelvic arch in the two known genera of Odontotormce exhibits 

 some interesting reptilian characters, one of which is seen also in 

 Hesjperomis. This portion of the skeleton is small in comparison with 

 the pectoral arch, corresponding to the difference in size between the 

 wings and the feet. 



The Sacrum. (Plates XXII, and XXVIII.) 



The sacrum is well preserved in the type specimen of IcMhyomis 

 dispar (number 1450), and appears to be composed of ten united verte- 

 brae. The centra of these vertebras are thoroughly coossified, and in the 

 anterior }Dart of the sacrum they are also considerably reduced in diameter. 

 The anterior articular face is slightly concave. The neural spin.es are 

 moderately developed in the anterior part, and are united with ossified 

 tendons, which diverge posteriorly, and form a flattened upper surface in 

 the median part of the sacrum. The middle part of the sacrum is much 

 crashed below, in the present specimen. The more posterior centra are of 

 moderate size, and the articular face of the last is depressed, and distinctly 

 concave. 



The transverse processes of the seventh sacral are well developed, 

 and stand nearly at right angles to the axis of the sacrum. Those of 

 the eighth and ninth are distant and divergent, those of the ninth vertebra 

 being directed strongly backward. The anterior three pairs of transverse 



