APPENDIX III 375 



NEPHROTOME (G. Tiephros, plus toma, a cut), the anlage of the kidney 



tubules; the mesomere. 

 NEUROCOEL (G. neuTon, a nerve, pkis koilos, hollow), the cavity of the 



nerve cord; homologous, and continuous, with the ventricles of the 



brain. 

 NEURON (G. a nerve), a combining form; neurone; neurology. 

 NiCTiT.ATiNG (L. nicititatus, from nicto, to wink), the third eyelid; moving 



from the anterior (median) margin toward the posterior; usually 



small in the mammal. 

 NOTO (G. iiotos, the back), a combining form; notochord. 

 NOTOCHORD (G. Tiotos, plus chordc, a string), the endodermal rod of tissue 



ventral to the nerve cord of the Chordata ; it becomes surrounded (or 



obliterated) by the mesodermal vertebrae. 

 NUCHA (L. nucha, nape of neck), a combining form in reference to the 



neck region; nuchal ligament; nuchal flexure of the brain. 



OBLONGATA (L. oh, before, plus longus, long), specifically the medulla 



oblongata. 

 OBTURATOR (L. ohturo, to close), a structure that closes off a passage; 



specifically, the structures which close the obturator foramen of the 



pelvis. 

 OCCIPUT (L. back of head); as adjective, the occipital region; or occipital 



bones, which surround the foramen magnum. 

 ocuLO (L. oculus, eye), a combining form; oculomotor; oculist. 

 ODON (G. odous, tooth), a prefix referring to teeth; as a suffix, don, or 



donl; odontoblast; homodont; thecodont. 

 OLFACTORY (L. olfactorium, a smelling bottle), pertaining to the sense of 



smell; olfactory nerves; olfactory capsule. 

 Oligocene (G. oligos, few or small, plus kainos, new), a geological period 



of Cenozoic time, following the Eocene. 

 OMENTUM (L. oment, a fold), an extension of the mesenteries which folds 



over the viscera. 

 OMO (G. shoulder), a combining form; omohyoid. 

 ONTO (G. being), a combining form; ontogeny; ontogenetic. 

 ONTOGENY (G. OTito, being, plus genesis, origin), the development of the 



individual; opposed to phylogeny, the development of the race. 

 opercular (L. operciil, a cover), a protective cover; specifically, the bony 



covering of the gills in fish above the elasmobranchs. 

 Ophidia (G. ophis, a serpent), a sub-order (or order) of reptiles, including 



the snakes. 

 ophthalmic (G. opJithalmos, eye), of or pertaining to the eye. 

 oral (L. OS, mouth), pertaining to the mouth. 

 ORBicuLO (L. orhis, a circle), a circular structure; specifically muscular; 



orbicularis oris of the mouth. 

 ORBIT (L. orbis, circle), specifically the eye socket; orbital ridges. 

 Ordovician (from Ordo vices, a Celtic tribe of Wales) ; a geological period 



of the early Paleozoic, between the Silurian and Devonian. 

 Ornithorhynchus (G. amis, a bird, plus rhis, nose), a genus of mono- 



treme mammals; the ''Duckbill Platypus". 

 orthogenesis (G. orthos, straight, plus genesis, beginning), the theory 



which considers evolution to have progressed in a straight line; rather 

 than as a fluctuating, branching development. 



