SKULL OF ICHTHYORNIS. 121 



The quadrate of Ichthyornis victor is represented in the cuts below, 

 figure 28. It is of large size, and in its general form does not differ 

 essentially from the quadrate in some modern birds. The undivided 

 articular head (figure 28, h) is its most important feature. 



FIGURE 28. — Quadrate bone of Ichthyornis victor. Marsh; twice Datural size. a. posterior view ; b. front view; 

 c. inner view; d. outer view; h. head; p. articulation for pterygoid; /. depression for jiigal. 



The skull of Ichthyornis has deep glandular depressions along the 

 roof of the orbits, similar to those on the cranium of Hesperomis, and some 

 recent water birds. The premaxillaiy bones are separate throughout 

 then posterior half, but were doubtless firmly united in front. The ante- 

 rior part of these bones has not been recovered, but the lower jaws would 

 seem to indicate that in some respects it resembled the beak of Hesperomis. 



In the type specimen (number 1450), the occipital condyle is sub- 

 trihedral in outline, when seen from behind. In another specimen (num- 

 ber 1459) this condyle is cordate in form, resembling the corresponding 

 part in Hesperomis. In most of its features, the base of the skull is more 

 like that of Hesperomis than of any modem birds. 



The Beain. 



The brain of Ichthyornis was remarkably small, and in its main 

 features, strongly reptilian. In form and proportions, it resembled the 

 brain of Hesperomis more nearly than that of any other known bud. The 

 figure given below represents an outline of the skull of Ichthyornis victor, 

 with a cast of the brain-cavity in position. A comparison of this figure with 

 that of the skull and brain of Hesperomis, represented on page 9, will show 

 the main points of resemblance. The most noticeable reptilian features 

 in the two brain-casts are the elongated form, and prominent optic lobes. 



