376 APPENDIX III 



ORTHOS (G. straight), a combining form; orthogenesis, Orthoptera, ortho- 

 pedic. 



osTEo (G. osteon, bone), a combining form; osteoblast; osteoclast; 

 osteology; 



OSTEOBLAST (G. osteou, plus blastos, a germ), a bone building cell; opposed 

 to osteoclast (G. klao, to break), a bone destroying cell. 



OSTIUM (L. ostium, a door), specifically the opening of the oviduct into 

 the body cavity. 



OsTRACODERMi (G. ostrac, shell, plus derma, skin), an extinct order of 

 armored vertebrates; they were formerly classified with the fish, but 

 are now generally considered as being more related to the cyclo- 

 stomes. 



OTIC (G. otikos, ear), pertaining to the ear; otic capsule. 



OTOLITH (G. otikos, ear, plus lithos, stone), a concretion in the utriculus 

 of the inner ear of some vertebrates, which stimulates impulses by 

 hitting the sensory hairs. 



OVARY (L. ovum, egg), the female gonad; the organ in which the repro- 

 ductive cells develop. 



OVIDUCT (L. ovum, egg, plus ductus, leading), the duct receiving the ova 

 and conducting them to the outside or to the uterus. 



OVUM (L. egg) ; plural ova; the female reproductive cell. 



oxYS (G. sharp), a combining form; Amphioxus. 



PALATAL (L. palatum, palate), relating to the palate; either hard palate, 



or soft palate. 

 Paleocexe (G. palaios, ancient, plus kainos, new), the most ancient of 



the Cenozoic strata; the first geological period following the Meso- 



zoic. 

 PALLIUM (L. jpalli, a mantle), a covering over a cavity; specifically, the 



roof of the cerebral hemispheres. See neopallium. 

 PANCREAS (G. -pas, all, plus kreas, flesh), a digestive gland emptying into 



the duodenum, with "islands" of endocrine tissue which secrete 



insulin. 

 PAPILLA (L. a nipple), any small, nipple-like structure; the papillae of the 



tongue; or, the mesodermal dental papilla which forms the dentine 



of the tooth. 

 PARA (G. para, besides), a combining form. 

 PARIETAL (L. paries, wall); the parietal bones of the skull; the parietal 



foramen. 

 PECTORAL (L. pectoralis, breast), relating to the upper thoracic region; pec- 

 toral muscles. 

 PELVIC (L. pelvis, a basin), pertaining to a pelvis; the bony girdle of the 



posterior limb ; the enlarged part of the ureter attached to the kidney. 

 PENIS (L.) the male copulatory organ, homologous with the clitoris of the 



female. 

 Pennsylvanian (from Pennsylvania, where first described), one of the 



later geological periods of Paleozoic times; the upper strata of the 



Carboniferous. See Mississippian. 

 PERI (G. around), a prefix; peripharyngeal grooves; pericardium. 

 PERICARDIAL (G. pcri, plus kurdia, heart), a membranous sac containing 



fluid surrounding the heart; morphologically a part of the body 



cavity. 



