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| mantle layer | The nuclear zone of the developing neural tube between the marginal layer and the ependymal layer; forms the gray matter of the central nervous system. Synonym: intermediate layer, mantle zone. (05 Mar 2000) |
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| manubriosternal joint | The early union, by hyaline cartilage, of the manubrium and the body of the sternum, which later becomes a symphysial type of joint. Synonym: synchondrosis manubriosternalis. (05 Mar 2000) |
| ventricular layer | An inner epithelial layer of cells bordering the lumen of the embryonic neural tube and brain, formed during the latter's stratification, and persisting in modified form throughout life. Synonym: ependymal zone, ventricular layer. (05 Mar 2000) |
| marginal layer | The outer, nonnuclear layer of the embryonic neural tube; into its fibrous network grow the longitudinal nerve fibres which eventually become the white matter of the cord and brain stem. Synonym: marginal zone. (05 Mar 2000) |
| germinative layer | The deepest layer of the epidermis, composed of dividing stem cells and anchoring cells. Synonym: basal cell layer, columnar layer, germinative layer, palisade layer, stratum basale, stratum cylindricum, stratum germinativum. (05 Mar 2000) |
| germinative layer of nail | The deeper layer of the nail that is continuous with the stratum germinativum of the surrounding skin and from which the nail plate is continuously formed. Synonym: germinative layer of nail. (05 Mar 2000) |
| germ layer | <embryology> A layer of cells produced during the process of gastrulation during the early development of the animal embryo, which is distinct from other such layers of cells, as an early step of cell differentiation. The three types of germ layers are the endoderm, ectoderm, and mesoderm. Diploblastic organisms (e.g. Coelenterates) have two layers, ectoderm and endoderm, triploblastic organisms (all higher animal groups) have mesoderm between these two layers. Germ layers become distinguishable during late blastula/early gastrula stages of embryogenesis and each gives rise to a characteristic set of tissues, the ectoderm to external epithelia and to the nervous system for example: although some tissues contain elements derived from two layers. (18 Nov 1997) |
| parietal layer | The outer layer of an enveloping sac or bursa, usually lining the walls of the cavity or space occupied by the enveloped structure, the structure itself being covered with the inner or visceral layer of the enveloping sac; an actual or potential space is enclosed by the two layers and intervenes between parietal and visceral layers. The parietal layer is usually the more substantial layer. Synonym: lamina parietalis. (05 Mar 2000) |
| germ layer theory | The developmental biology theory that during early development, the animal embryo divides itself into two or three germ layers, each of which then proceed to further differentiate into organs and tissues specific to that particular layer. (09 Oct 1997) |
| parietal layer of leptomeninges | Like a cobweb, covered with or consisting of soft fibres or hairs so entangled as to give a cobwebby appearance. (09 Oct 1997) |
| parietal layer of serous pericardium | The outer part of the serous pericardium suported by the fibrous pericardium. Synonym: lamina parietalis pericardii. (05 Mar 2000) |
| parietal layer of tunica vaginalis | The outer part of the tunica vaginalis testis supported by the internal spermatic fascia. Synonym: lamina parietalis tunicae vaginalis testis. (05 Mar 2000) |
| carpometacarpal joint of thumb | The saddle-shaped synovial articulation between the trapezium and the base of the first metacarpal bone. Synonym: articulatio carpometacarpea pollicis. (05 Mar 2000) |
| cartilaginous joint | A joint in which the apposed bony surfaces are united by cartilage; they are divided into synchondroses and symphyses; in synchondroses, the cartilage connecting the apposed surfaces is, as a rule, ultimately converted to bone, as between epiphyses and diaphyses of long bones; exceptions are the sternal synchondroses and the cartilaginous union of the first rib and the manubrium of the sternum; in symphyses the bones are connected by a flat disk of fibrocartilage which remains unossified throughout life; e.g., the intervertebral disk and the symphysis pubis. Synonym: articulatio cartilaginis, cartilaginous articulation, junctura cartilaginea, synarthrodial joint. (05 Mar 2000) |
| ginglymoid joint | A uniaxial joint in which a broad, transversely cylindrical convexity on one bone fits into a corresponding concavity on the other, allowing of motion in one plane only, as in the elbow. Synonym: ginglymus, ginglymoid joint. (05 Mar 2000) |