140 GLOSSAEY. 



nearly with the C&lelmlnlMa or Eniozoa Cavitaria of Cuvier and the 



KematelmintMx of Vogt. It includes the parasitic " Thread Worms " and 



" Round Worms," and tlie Gordiacea may be placed under the same head. 

 NERVE (nervus, vevpuv), originally a sinew or tendon : after Galen's time applied 



to the conducting branches of the Sensori-motor apparatus. 

 NECROPTERA (vtvpov, a cord ; irTtpSv, wing), an order of insects in which the four 



membranous wings are supported by strong ribs or nervures. 

 NOTOCHORD (VUTOV, back; xP^- a string), or Chorda dorsalis, an embryonic structure 



in Vertebrata formed immediately under the primitive groove, and usually 



replaced by the spinal column in the adult. 

 NUCLEUS (a kernel, fr. nux : dim. nucleolus), a speck of germinal matter found 



normally in cells. 

 ODONTOIDES (sc. proeessus ; oSofo, tooth ; e!8oy, form), the body of the atlas, which 



is separate from it and usually ankylosed with the axis. 

 OUONTOPHORA < oSovs, tooth ; (pepta, bear), those classes of Mottusca which have 



heads and a peculiar tooth-bearing apparatus. 



(ESOPHAGUS (ofo-os, a reed ; <(>ay?i>, to eat), the gullet Arid, de Part. An. iii. 3. 

 OMPHALOS (6fj.<pa\6s= umbilicus), the navel, i.e., the scar left in the abdomen of a 



mammal, where the umbilical cord was attached. 

 OOSTEGITE (u6v, egg; o-Teyca, to cover), scales or otlier parts of Annulosa modified 



so as to protect the eggs while carried by the mother. 

 OPERCULUM (fr. operio~), a covering : in fish a bony flap (possibly homologous with 



the external ear of Mammals) which covers over the gills ; in univalve Mol- 



lusks a concretion which closes the shells. 



OPHIDIA (8$ts, a serpent), an order of Reptiles : Serpentes of Linnaeus. 

 OPHIUBA (o<f>s, snake ; ovpd, a tail), " Brittle star," a genus of Echinodermata, 



giving its name to the order Ophiuridea. 

 OPISTHOTIC (oiriffQev, behind ; o3s, the ear), the posterior ossification of the auditory 



capsule, corresponding with the mastoid and part of the petrous bones in 



Man. 

 OPTIC LOBES, the ganglia of the brain in Vertebrata to which the optic nerves lead 



in all but the Marsipobranchii and Amphioxus : they are single on each side 



in the lower classes, and called Corpora Ingemina ; double in the higher ones, 



and called C. quadrigemina, or Nates and Testes. 

 ORBITOSPHENOID (orbitus, dim. of orbs; sphenoides), part of the third cranial 



segment, corresponding with the alte minores or processes of Ingrassias in 



human anatomy, and always forming the back of the orbit. Cf. ALISPHENOID. 

 ORNITHODELPHIA (opvis, bird ; SeA<j>us, womb), the subclass represented by the 



order Monotremata. 

 ORNITHOUHYNCUIS (upvis, a bird; pvy%os, a beak), a genus of Monolremata, 



otherwise called the Duck-billed Platypus (broad, i. e., webbed-foot), or Water 



Mole. 



ORTHOPTERA (6p86s, straight ; irrep^v, wing), an order of Insects. 

 OSTRACODA (offTpaKcbSys, adj. fr. oa-TpaKov, a shell), an order of Crustacea enclosed 



in a hard carapace. 

 OTOUTHS (o3s, ear ; Afflor, stone), small bones found suspended in the internal 



ear of fishes, corresponding with the otoconium or " ear-dust " of Man. The 



term is also applied to similar concretions in the auditory sacs of Crustacea 



and other invertebrate animals. 



OXYURIS (o|us, sharp ; ovpd, tail), thread-worm, one of the Nematoidea. 

 PACHYDERMATA (TTOXVS, thick ; Sfpfj.a, skin), a Mammalian order of Cuvier's, nearly 



