INDEX. 



431 



Onychodus, 249. 

 Operculum, 23, 161. 

 Ophiderpeton, 283. 

 Ophidia, 322. 

 Ophidiidae, 261. 

 Ophidium, 261. 

 Ophidioida, 261. 

 Ophiocephalidae, 262. 

 Ophisaurus, 320. 

 Ophthalmicus nerve, 61, 62. 

 Opisthocoelous, 139. 

 Gpisthocomi, 349. 

 OpisVhoglypha, 325. 

 Opisthomyzon, 263. 

 Opisthotic, 158. 

 Opoderodonta, 326. 

 Opossums, 379. 

 Optic chiasma, 61. 

 Optic lobes, 50. 

 Optic nerves, 60. 

 Optic stalk, 78. 

 Optic thalami, 49. 

 Optic tract, 61. 

 Optic vesicle, 78. 

 Orang-utan, 416. 

 Orbitosphenoid, 158. 

 Orca, 408. 

 Oreodon, 398. 

 Oreodontidae, 398. 

 Organ of Corti, 73. 

 Organ of Giraldi, 130. 

 Organ of Jacobson, 77. 

 Origin of muscle, 112. 

 Ornithopoda, 317. 

 Ornithodelphia, 376. 

 Ornithorhynchidae, 376. 

 Ornithorhynchus, 376. 

 Ornithosauria, 329. 

 Oronasal groove, 76. 

 Orthagoriscus, 267. . 

 Orthopoda, 316. 

 Orycteropodidae, 382. 

 Orycteropus, 382. 

 Oryx, 399. 

 Os en ceinture, 278. 

 Os entoglossum, 161. 

 Os lenticulare, 159. 

 Os magnum, 177. 

 Os orbiculare, 159. 

 Os trans versum, 163. 

 Oscines, 351. 

 Osmerus, 256. 

 Osphromenus, 262. 

 Ossicula auditus, 158. 



