372 



AN INTRODUCTION TO THE STUDY OF FOSSILS 



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Fig. i6i. — Ichthyornis victor Marsh, from the marine Niobrara beds (mid-Creta- 

 ceous) of western Kansas. It was slightly larger than a common pigeon. The 

 hollow bones, strongly keeled breastbone and large wings indicate this to have 

 been an excellent flyer, while its association with such universally marine forms 

 as ammonites shows that it must have lived at least upon the borders of the sea. 

 Though similar in general appearance to living birds, yet it shows its ancestry 

 in its small, elongate, reptile-like brain (compare figures B, C, D, all drawn to same 

 scale) and in its sharp, pointed, recurved teeth which are lodged in distinct sockets. 

 A, restoration of entire skeleton. B, outline of the skull and brain cavity of the 

 modern tern, seen from above. C, same view of Ichthyornis victor. D, cast of 

 brain cavity of a young alligator, ar., articular bone or mandible; c, cerebrum; 

 cb., cerebellum; ca., carpal (wrist) bones; cl., clavicle (the " wish bone"); co., 

 coracoid ; dn., dentary bone of mandible ; fi., fibula, — very small as in all modern 

 birds; hii., humerus; il., iHum, — the hipbone; is., ischium; m., medulla; 

 max., maxilla ; m.ca., metacarpals ; ob., orbit of eye ; ol., olfactory lobes of brain ; 

 op., optic lobes of brain ; ph., phalanges (digit II has two phalanges) ; /«., pubis; 

 r., rib; ra., radius; ti.la., tibio-tarsals, — the union of the tibia and proximal row 

 of tarsals as is seen in the development of modern birds; t.m.ta., tarso-metatarsal 

 bones, — union of the distal row of tarsals with the metatarsals as is shown in the 

 young of modern birds; ul., ulna; /, //, etc., digits, ist (corresponding to the 

 thumb and great toe), 2d, etc. (After Marsh.) 



