| external nuclear layer of retina | The outermost layer of the cerebral layer of retina, composed of the primary receptor cells of the retina; the stratum consists of two sublayers: 1) an external layer made up of the rods and cones, the photosensitive processes of the receptor cells, and 2) the external nuclear layer containing the cell bodies of these cells; the external limiting membrane forms a perforated supporting plate between the two sublayers; the name refers to the fact that the retinal receptor cells are a specialised form of (epithelial) ependyma cell and thus, in a sense, are comparable to the neuroepithelial cells (e.g., hair cells) of other sense organs. Synonym: external nuclear layer of retina, stratum neuroepitheliale retinae, stratum nucleare externum retinae. (05 Mar 2000) |
|---|---|
| external oblique | <anatomy, muscle> Origin, fifth to twelfth ribs; insertion, anterior half of lateral lip of iliac crest, inguinal ligament, and anterior layer of the rectus sheath; action, diminishes capacity of abdomen, draws thorax downward; nerve supply, thoracoabdominal nerves. Synonym: musculus obliquus externus abdominis, abdominal external oblique muscle. (05 Mar 2000) |
| external oblique reflex | Contraction of the external oblique and rectus abdominis muscles upon tapping the anterior and outer part of the lower thoracic wall. (05 Mar 2000) |
| external oblique ridge | A horizontal bony crest on the external surface of the body of the mandible, inferior to the alveolar bone, marking the site of attachment of the buccinator muscle. (05 Mar 2000) |
| external obturator muscle | <anatomy, muscle> Origin, lower half of margin of obturator foramen and adjacent part of external surface of obturator membrane; insertion, trochanteric fossa of greater trochanter; action, rotates thigh laterally; nerve supply, obturator. Synonym: musculus obturator externus, external obturator muscle. (05 Mar 2000) |
| external occipital crest | A ridge extending from the external occipital protuberance to the border of the foramen magnum. Synonym: crista occipitalis externa, linea nuchae mediana. (05 Mar 2000) |
| external occipital protuberance | A prominence about the centre of the outer surface of the squamous portion of the occipital bone, giving attachment to the ligamentum nuchae. Synonym: protuberantia occipitalis externa. (05 Mar 2000) |
| external opening of urethra | The slitlike opening of the urethra in the glans penis, the external orifice of the urethra (in the female) in the vestibule, usually upon a slight elevation, the papilla urethrae. Synonym: ostium urethrae externum, external opening of urethra, meatus urinarius, orificium urethrae externum. (05 Mar 2000) |
| external ophthalmopathy | Any disease of the conjunctiva, cornea, or adnexa of the eye. (05 Mar 2000) |
| external ophthalmoplegia | Paralysis affecting one or more of the extrinsic eye muscles. Synonym: external ophthalmoplegia. (05 Mar 2000) |
| external os of uterus | The vaginal opening of the uterus. Synonym: ostium uteri, mouth of the womb, opening of uterus, orificium externum uteri, os uteri externum, ostium uteri externum. (05 Mar 2000) |
| external ovular transmigration | Direct ovular transmigration occurs when the ovum passes across the pelvic cavity. (05 Mar 2000) |
| external pacemaker | An artificial cardiac pacemaker whose electrodes for delivering rhythmical electrical stimuli to the heart are placed on the chest wall. (05 Mar 2000) |
| external phase | The medium or fluid in which a disperse is suspended. Synonym: continuous phase, dispersion medium, dispersion phase, external medium. (05 Mar 2000) |
| external pin fixation | In oral surgery, stabilization of fractures of the mandible, maxilla, or zygoma by pins or screws drilled into the bony part through the overlying skin and connected by a metal bar. Pin fixation by replacing the rigid metal bar connector with an acrylic bar adapted at the time of reduction of the fracture. (05 Mar 2000) |