GLOSSARY. 103 
Odontoid (Gr. odous, a tooth ; ezdos, shape).— Applied 
to a process, tooth-like in shape, of the second 
cervical vertebra. 
Oleecranon (Gr. olexe, the elbow ; ranion, the top 
of the head).— The summit of the ulna, 
which forms the elbow. 
Olivary eminence (L. olive-shaped)—An eminence 
in mammals on the superior surface of the 
body of the basi-sphenoid. 
Omosternum (Gr. omos, the shoulder; sternon, the 
breast).—A median process developed from 
the coraco-scapula cartilages in the Batrachia. 
Operculum (L. a lid).—The gill cover or bony flap 
covering and protecting the gills in many 
fishes. 
Opisthoceelus (Gr. ofzsthen, behind ; £oz/os, hollow).— 
Applied to those vertebre the centra of 
which are concave posteriorly. 
Opisthotie (Gr. opzsthen, behind ; ous, otos, the ear).— 
An ossification of the temporal bone surround- 
ing the fenestra rotunda and cochlea. In 
Teleostean fishes it persists as a separate 
bone. 
Orbito-sphenoid (L. ovdzto, the orbit; Gr. sphen, a 
wedge ; ezdos, shape)—A bone of the skull 
in front of the optic foramen, in human 
anatomy termed the lesser wing of the 
sphenoid bone. 
Os articulare (L. articular bone)—A bone in the 
mandible in some Vertebrata. 
