A flexible rod-shaped body found in embryos of all chordates. It is composed of cells derived from the mesoderm and defines the primitive axis of the embryo. In some chordates, it persists throughout life as the main axial support of the body, while in most vertebrates it becomes the nucleus pulposus of the intervertebral disc. The notochord is found ventral to the neural tube.
notochord posterior region
notochordal canal
nucleus pulposus
nuptial pad
obturator foramen
obturator process of ischium
ocular fundus
ocular surface region +
oculomotor nerve
odontode +
olecranon
olecranon fossa
olfactory apparatus chamber +
olfactory nerve
olivary body +
omentum +
opercular part of inferior frontal gyrus
ophthalmic nerve +
opisthosome
opisthotic
optic cup +
optic disc
optic foramen +
optic vesicle +
ora serrata of retina
oral cirrus
orbital part of frontal bone
orbitosphenoid +
orbitosphenoid septum
organ part +
oronasal membrane
os clitoris
os penis
osseus cochlea +
osseus cochlear canal
osseus labyrinth vestibule +
osseus semicircular canal
osseus spiral lamina
otic capsule +
otic vesicle protrusion +
otolith +
otolith organ +
otolithic part of statoconial membrane +
outer medulla vasa recta ascending limb
outer medulla vasa recta descending limb
outer root sheath companion layer
outflow tract +
outflow tract pericardium
ovarian follicle +
ovarian ligament
Pacinian corpuscle
pair of dorsal aortae
paired fin radial element +
paired fin radial skeleton +
paired limb/fin field +
paired limb/fin skeleton +
palpebral fissure
papillary layer of dermis +
papillary muscle of heart +
parafoveal part of retina
parapineal organ
parasagittal crest
parasphenoid flange
parenchyma of central nervous system +
parenchyma of mammary gland
parenchyma of spleen +
parietal organ
parietal serous membrane +
pars amphibiorum
pars basilaris
pars cylindriformis ilei
pars inferior of labyrinth
pars intermedia of adenohypophysis
pars plana of ciliary body
pars plicata of ciliary body
pars reflexa of masseter
pars tuberalis of adenohypophysis
part of afferent arteriole forming the juxtaglomerular complex