A sheet of one substance lying on another and distinguished from it by a difference in texture or color or by not being continuous with it. SEE ALSO: stratum, lamina. SYN: panniculus.
- anterior limiting l. of cornea a transparent homogeneous acellular l., 6 to 9 μm thick, lying between the basal lamina of the outer l. of stratified epithelium and the substantia propria of the cornea; considered to be a basement membrane. SYN: anterior elastic l., Bowman l., Bowman membrane, lamina elastica anterior, lamina limitans anterior corneae.
- anterior l. of rectus sheath [TA] the portion of the rectus sheath that lies anterior to the muscle, consisting in its upper two-thirds of contributions from the aponeuroses of the external and internal oblique muscles, and in its lower third (below the arcuate line) of contributions from the aponeuroses of all three muscles of the anterolateral abdominal wall. SYN: lamina anterior vaginae musculi recti abdominis.
- anterior l. of thoracolumbar fascia [TA] fascial membrane extending from transverse processes of lumbar vertebrae. SYN: lamina anterior fasciae thoracolumbalis [TA], fascia musculi quadrati lumborum, lamina profunda fasciae thoracolumbalis, quadratus lumborum fascia.
- bacillary l. SYN: l. of rods and cones.
- basal l. SYN: stratum basale (1).
- blastodermic layers the primordial cell layers on the yolk surface of a telolecithal egg; in the earliest stages they consist of protoderm, and then later differentiate into ectoderm, endoderm, and mesoderm.
- brown l. SYN: suprachoroid lamina of sclera.
- cambium l. 1. the inner osteogenic l. of the periosteum; 2. a highly cellular zone immediately beneath the epithelium covering a botryoid sarcoma.
- cerebral l. of retina the internal l. of the retina containing the neural elements, as distinguished from the outer leaf of the retina, or pigmented l.. SYN: pars optica retinae [TA], neural l. of retina, stratum cerebrale retinae.
- Chievitz l. in the developing retina of an embryo, a transitory zone between the inner and outer neuroblastic layers that is devoid of nuclei.
- circular l. of detrusor (muscle) of urinary bladder [TA] the substantial middle l. of three ill-defined, interlacing layers (the inner and outer layers being predominantly longitudinally oriented) of smooth (involuntary) muscle fibers constituting the muscle l. of the wall of the bladder. SYN: stratum circulare musculi detrusoris vesicae [TA].
- circular l. of muscle coat of small intestine [TA] the inner l. of smooth (involuntary) muscle of the muscle coat (muscularis externa) of the small intestine in which the muscle fibers encircle the lumen; it is claimed by some investigators that the orientation of the muscle fibers is a tight spiral or helix rather than being truly circular. SYN: stratum circulare tunicae muscularis intestini tenuis [TA], short pitch helicoidal l., stratum helicoidale brevis gradus.
- circular l. of muscular coat [TA] the inner, circular l. of the smooth muscle of the muscular coat. Terminologia Anatomica lists circular layers of muscular coats (stratum circulare tunicae muscularis ...) of the following: 1) colon (... coli [TA]); 2) prostatic urethra (... urethrae prostaticae [TA]); 3) rectum (... recti [TA]); 4) small intestine (... intestini tenuis [TA]); 5) stomach (... gastricae [TA]); 6) urethra (... urethrae [TA]). SYN: stratum circulare tunicae muscularis [TA].
- claustral l. the l. of subcortical gray matter between the external capsule and the white matter of the insula or extreme capsule.
- clear l. of epidermis SYN: stratum lucidum.
- columnar l. SYN: stratum basale epidermidis.
- conjunctival l. of eyelids SYN: palpebral conjunctiva.
- deep l. [TA] in a stratified structure, the stratum which lies beneath all others, furthest from the surface. See deep l. of levator palpebrae superioris, deep l. of temporal fascia. SYN: lamina profunda [TA], deep lamina.
- deep gray l. of superior colliculus [TA] a l. of cell bodies in the superior colliculus located between the intermediate white l. and the deep white l.. SYN: stratum griseum profundum colliculis superioris [TA].
- deep l. of levator palpebrae superioris the deeper fibers of the levator muscle of the superior eyelid that are inserted into the superior tarsal plate. SYN: lamina profunda musculi levatoris palpebrae superioris.
- deep l. of temporal fascia the deep part of the temporal fascia attaching to the medial surface of the zygomatic arch. SYN: lamina profunda fasciae temporalis [TA].
- deep white l. of superior colliculus a l. of neuron cell bodies in the superior colliculus located between the deep white l. and the intermediate white matter. SYN: stratum medullare profundum [TA].
- deep white l. [TA] of superior colliculus [TA] the innermost l. of the superior colliculus; a l. of myelinated fibers located internal to the deep gray l..
- layers of dentate gyrus [TA] from the surface of the dentate gyrus, these layers are: the molecular l. [TA] (stratum moleculare [TA]), which contains dendrites of granular cells and some incoming axons from the perforant pathway, granular l. [TA] (stratum granulare [TA]), which contains the l. of small granular cells, and the multiform l. [TA] (stratum multiforme [TA]), also sometimes called the polymorphic l., which contains axons of granular cells and some afferent axons entering via the fornix. SYN: strata gyri dentati [TA].
- enamel l. SYN: ameloblastic l..
- ependymal l. an inner epithelial l. 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. SYN: ependymal zone, ventricular l..
- episcleral l. of fibrous l. of eyeball [TA] the delicate moveable l. of loose connective tissue between the external surface of the sclera and the fascial sheath of the eyeball. SYN: lamina episcleralis [TA], episcleral lamina.
- epithelial layers epithelium.
- epitrichial l. the superficial flattened-cell l. of the epidermis of a young embryo before the definitive stratification has developed.
- fatty l. of subcutaneous tissue [TA] superficial portion of the subcutaneous tissue of certain areas of the body (e.g., inferior portion of anterior abdominal wall) which is specialized for fat storage and thus often has an abundance of fat, especially in the overnourished individual, compared with the deeper, fibrous portion of the subcutaneous tissue; in morbid obesity, this l. forms the core of a large, sagging apronlike fold. SEE ALSO: fatty l. of subcutaneous tissue of abdomen. SYN: panniculus adiposus [TA].
- fatty l. of subcutaneous tissue of abdomen [TA] the more superficial, fatty part of the superficial fascia of the lower anterior abdominal wall. SYN: panniculus adiposus telae subcutaneae abdominis [TA], Camper fascia, fatty l. of superficial fascia.
- fibromusculocartilagenous l. of bronchi [TA] l. between submucosa and adventitia of bronchi which includes cartilages enclosed in perichondrium continuous between cartilages with a dense, fibrous membrane that includes smooth muscle and elastic fibers; this l. provides rigidity to the wall while allowing active reduction and passive increase in diameter of the bronchus. SYN: tunica fibromusculocartilaginea bronchi [TA].
- fibrous l. of eyeball [TA] the outer l. of the eyeball composed of the sclera and cornea. SYN: tunica fibrosa bulbi [TA], fibrous tunic of eye, tunica externa oculi.
- fibrous l. of joint capsule [TA] the outer fibrous part of the capsule of a synovial joint, which may in places be thickened to form capsular ligaments. SYN: membrana fibrosa capsulae articularis [TA], fibrous l. of articular capsule, fibrous membrane of joint capsule, fibrous articular capsule, stratum fibrosum capsulae articularis.
- fibrous l. in or on deep aspect of fatty l. of subcutaneous tissue [TA] fibrous tissue interspersed within or concentrated in the deeper portions of the otherwise fatty l. of subcutaneous tissue in a particular region, making it more substantial, but not organized into a uniform, membranous l.. SYN: stratum fibrosum panniculi adiposi telae subcutaneae [TA].
- fillet l. SYN: stratum lemnisci.
- ganglionic l. [TA] the l. of the retina containing primarily the cell bodies of ganglion cells, although some amacrine cell bodies are also found. SEE ALSO: ganglion cells of retina, under cell. SYN: stratum ganglionicum [TA], ganglionic cell l. of retina.
- ganglionic l. of optic nerve obsolete term used to describe the multipolar neurons in the retina that give rise to the fibers of the optic nerve. SYN: stratum ganglionare nervi optici.
- germ l. one of the three primordial cell layers (ectoderm, endoderm, mesoderm) established in an embryo during gastrulation.
- germinative l. SYN: stratum basale epidermidis.
- glomerular l. of olfactory bulb a l. composed of spherical bodies, called glomeruli, formed by the synapses of mitral cells with the olfactory nerve fibers derived from the cells of the olfactory epithelium.
- granular l. of cerebellum [TA] the deepest of the three layers of the cortex; it contains large numbers of granule cells, the dendrites of which synapse with incoming mossy fibers in cerebellar glomeruli. Thin, unmyelinated axons of granule cells ascend perpendicularly into the molecular l. in which they bifurcate into fibers coursing parallel to the long axis of the cerebellar folia. Parallel fibers form numerous synapses with the dendrites of Purkinje cells, basket cells, and stellate cells. SYN: granular l. of cerebellar cortex [TA], stratum granulosum corticis cerebelli [TA].
- granular l. of epidermis a l. of somewhat flattened cells containing basophilic granules of keratohyalin and lying just above the stratum spinosum and deep to the stratum corneum. SYN: stratum granulosum epidermidis.
- gray layers of superior colliculus term applied to any one of the three major layers of gray matter of the superior colliculus that alternate with layers composed chiefly of nerve fibers: 1) the superficial gray l. of superior colliculus, external to the largely white l. of the incoming fibers of the optic tract (optic l.); 2) the intermediate gray l. of superior colliculus, placed between the optic l. and a more deeply located l. of fibers, the stratum lemnisci; 3) the deep gray l. of superior colliculus, between the stratum lemnisci and the central gray substance surrounding the cerebral aqueduct, and containing the large nerve cells from which most of the colliculus descending connections (tectobulbar, tectopontine, and tectospinal tract) originate. SYN: stratum cinereum colliculi superioris, stratum griseum colliculi superioris.
- half-value l. (HVL) the thickness of a specific absorber ( e.g., aluminum) that will reduce the intensity of a beam of radiation to one-half its initial value.
- layers of hippocampus [TA] four layers formed by cells and cell processes; they are, beginning at the alveus and ventricular surface : the oriens l. [TA] (stratum oriens [TA]) which contains basal dendrites and axon collaterals of the pyramidal cells, pyramidal l. [TA] (stratum pyramidale [TA]) which contains the sonata of the large pyramidal cells of the hippocampus, radiant l. [TA] (stratum radiatum [TA]) which contain the branching dendrites of the pyramidal cells and recurrent axon collaterals of the pyramidal cells, and the lacunar-molecular l. [TA] (stratum moleculare et substratum lacunosum [TA]) which contains the distal dendrites and some of the incoming axons of the preforant pathway. SYN: strata hippocampi [TA].
- Huxley l. a l. of cells interposed between Henle l. and the cuticle of the inner root sheath of the hair follicle. SYN: Huxley membrane, Huxley sheath.
- infragranular l. the cellular band deep to the inner granular l. of the developing human cerebral cortex, which differentiates into the ganglionic l. and multiform l. by the sixth fetal month.
- inner l. of eyeball [TA] the third and deepest of the three layers of the eyeball, composed of the retina, intraocular part of the optic nerve, and the retinal blood vessel s. SYN: tunica interna bulbi [TA], nervous tunic of eyeball.
- inner limiting l. [TA] the membranelike structure located immediately internal to the l. of nerve fibers; composed of the processes of the neuroglial cells (Müller cells) of the retina. SYN: stratum limitans internum [TA].
- inner nuclear l. [TA] the l. of the retina composed of the cell bodies of bipolar cells, horizontal cells, and some of the cell bodies of amacrine cells. SYN: stratum nucleare internum [TA].
- l. of inner and outer segments [TA] the l. of the retina located external to the outer limiting membrane and composed of the inner and outer segments of the rods and cones; the outer tips of the rod and cone segments are apposed to the pigmented l.. SYN: stratum segmentorum externorum et internorum [TA].
- inner plexiform l. [TA] the l. of the retina composed of the processes of bipolar cells, ganglion cells, and amacrine cells; a l. containing synaptic contacts. SYN: stratum plexiforme internum [TA].
- intermediate l. SYN: mantle l..
- intermediate white l. [TA] of superior colliculus [TA] a l. of myelinated fibers located between the intermediate and deep gray layers of the superior colliculus. SYN: stratum medullare intermedium [TA].
- investing l. [TA] a fascial l. that ensheathes or intimately encloses a specific group of muscles. SYN: fascia investiens [TA].
- investing l. of cervical fascia [TA] the part of the cervical fascia investing the sternocleidomastoid and trapezius muscles and completely encircling the neck. SYN: lamina superficialis fasciae cervicalis [TA], superficial l. of deep cervical fascia, investing fascia.
- lacunar-molecular l. [TA] See layers of hippocampus. SYN: stratum moleculare et substratum lacunosum [TA].
- Langhans l. SYN: cytotrophoblast.
- limiting layers of cornea See anterior limiting l. of cornea, posterior limiting lamina of cornea.
- longitudinal l. of muscle coat of small intestine [TA] longitudinal l. of muscular coat of small intestine. SYN: stratum longitudinale tunicae muscularis intestini tenuis [TA], stratum helicoidale longi gradus.
- longitudinal l. of muscular coat [TA] the outer, longitudinal l. of the smooth muscle of the muscular coat. Terminologia Anatomica lists longitudinal layers of muscular coats (stratum longitudinale tunicae muscularis ...) of the following: 1) intermediate urethra (... urethrae intermediae [TA]); 2) colon (... coli [TA]); 3) prostatic uretra (... urethrae prostaticae [TA]); 4) rectum (... recti [TA]); 5) small intestine (... intestini tenuis [TA]); 6) spongy urethra (... urethrae spongiosae [TA]); 7) stomach (... gastricae [TA]). SYN: stratum longitudinale tunicae muscularis [TA].
- malpighian l. SYN: malpighian stratum.
- mantle l. the nuclear zone of the developing neural tube between the marginal l. and the ependymal l.; forms the gray matter of the central nervous system. SYN: intermediate l., mantle zone (1).
- marginal l. the outer, nonnuclear l. of the embryonic neural tube; into its fibrous network grow the longitudinal nerve fibers that eventually become the white matter of the spinal cord and brainstem. SYN: marginal zone (2).
- membranous l. of subcutaneous tissue of abdomen [TA] the deeper, membranous or lamellar part of the subcutaneous tissue of the lower abdominal wall; it is continuous with the superficial perineal (Colles) fascia. SYN: membranous l. of superficial fascia of perineum (2), membranous l. of superficial fascia (2), Scarpa fascia.
- membranous l. of superficial fascia 1. SYN: subcutaneous tissue of perineum. 2. SYN: membranous l. of subcutaneous tissue of abdomen.
- membranous l. of superficial fascia of perineum 1. SYN: subcutaneous tissue of perineum. 2. SYN: membranous l. of subcutaneous tissue of abdomen.
- molecular l. term applied to any l. of brain tissue that contains few nerve-cell bodies and is composed largely of terminal arborizations of dendrites and axons; notable examples are the superficial l. (first l.) of the cerebral cortex and the molecular l. of cerebellum. SYN: plexiform l., stratum moleculare.
- molecular l. of cerebellar cortex [TA] the outer lamina of the cortex, containing the cell bodies (unless the Purkinje cell l. is designated as a separate l.) and dendrites of Purkinje cells, the axons of the granule cells, and the cell bodies, dendrites, and axons of basket cells. SYN: stratum moleculare corticis cerebelli [TA], molecular l. of cerebellum.
- molecular l. of cerebral cortex [TA] l. 1 of the cortex cerebri. SYN: lamina molecularis corticis cerebri [TA], plexiform l. of cerebral cortex.
- molecular layers of olfactory bulb the layers, composed mainly of nerve fibers, on the outer and inner sides of the l. of mitral cells of the bulb.
- molecular l. of retina name applied to each of the plexiform layers of the retina. SYN: stratum moleculare retinae.
- multiform l. [TA] of cerebral cortex the innermost l. of the cerebral cortex, l. XI. SYN: fusiform l., polymorphous l., spindle-celled l..
- muscle l. in fatty l. of subcutaneous tissue [TA] l. of smooth or striated muscle embedded within the fatty subcutaneous tissue for contraction or to produce movement of the skin, e.g., facial muscles within subcutaneous tissue of face and neck, dartos muscle within the dartos fascia of scrotum. SYN: stratum musculosum panniculi adiposi telae subcutaneae [TA].
- muscular l. [TA] the muscular, usually middle, l. of a tubular structure; for most of the gastrointestinal tract, it consists of an outer longitudinal l. of muscle and an inner circular l.. SYN: tunica muscularis [TA], muscular coat.
- muscular l. of bronchi muscular l. of the bronchial wall. SYN: tunica muscularis bronchiorum [TA], muscular coat of bronchi.
- muscular l. of colon [TA] muscular l. of the wall of the colon. SYN: tunica muscularis coli [TA], muscular coat of colon.
- muscular l. of ductus deferens [TA] muscular l. of the wall of the ductus deferens. SYN: tunica muscularis ductus deferentis [TA], muscular coat of ductus deferens.
- muscular l. of esophagus [TA] muscular l. of the esophageal wall. SYN: tunica muscularis esophagi [TA], muscular coat of esophagus.
- muscular l. of female urethra [TA] muscular l. of the wall of the female urethra. SYN: tunica muscularis urethrae femininae [TA], muscular coat of female urethra.
- muscular l. of gallbladder muscular tunic of the gallbladder, consisting of layers of smooth muscle fibers coursing in various directions immediately external to the mucosa of the gallbladder. SYN: tunica muscularis vesicae biliaris [TA], muscular coat of gallbladder, tunica muscularis vesicae felleae, muscular tunic of gallbladder.
- muscular l. of intermediate part of (male) urethra [TA] relatively thin inner coat of smooth (involuntary) muscle bundles, mostly longitudinally arranged and separated from the epithelium by a thin vascular stroma of fibroelastic connective tissue, which are continuous superiorly with those of the prostatic urethra and peripherally with an outer, much more prominent l. of circularly oriented skeletal (voluntary) muscle fibers that forms the main, tubelike part of the external urethral sphincter. SEE ALSO: external urethral sphincter of male. SYN: tunica muscularis partis intermediae urethrae masculinae [TA], muscular coat of intermediate part of male urethra.
- muscular l. of large intestine [TA] muscular l. of the wall of all parts of the large intestine (cecum, colon, rectum, and anal canal) collectively. SYN: tunica muscularis intestini crassi [TA], muscular coat of large intestine.
- muscular l. of male urethra [TA] muscular l. of the prostatic, intermediate, and spongy segments of the male urethra. SEE ALSO: muscular l. of intermediate part of (male) urethra. SYN: tunica muscularis urethrae masculinae [TA], muscular coat of male urethra.
- muscular l. of pharynx [TA] muscular l. of the pharyngeal wall. In contrast with the muscular coats of the rest of the gastrointestinal tract (except anal canal), that of the pharynx has an outer circular l. and an inner longitudinal l.. SYN: tunica muscularis pharyngis [TA], muscular coat of pharynx.
- muscular l. of prostatic urethra [TA] relatively thin inner coat of smooth (involuntary) muscle bundles, both circularly and longitudinally arranged and separated from the epithelium by a thin vascular stroma of fibroelastic connective tissue, which are continuous inferiorly with those of the intermediate urethra and peripherally with the fibromuscular tissue of the prostate, including a relatively thick, troughlike l. of skeletal (voluntary) muscle that ascends the anterior aspect of the prostatic urethra to the neck of the bladder as part of the external urethral sphincter; proximal (superior) to the seminal colliculus, which bears the openings of the ejaculatory ducts, the circular l. of smooth muscle is especially prominent as a continuation of the internal urethral sphincter of the intramural or preprostatic part of the urethra. SEE ALSO: external urethral sphincter of male, internal urethral sphincter. SYN: tunica muscularis partis prostaticae urethrae masculinae [TA], muscular coat of intermediate part of male urethra, muscular coat of prostatic urethra.
- muscular l. of rectum [TA] muscular l. of the wall of the rectum. SYN: tunica muscularis recti [TA], muscular coat of rectum.
- muscular l. of renal pelvis [TA] middle l. (between outer adventitia and inner mucosa) composed of two morphologically and histochemically distinct types of smooth (involuntary) muscle fibers, one of which is identical and continuous with that of the ureters, while the other is unique to the calices and pelvis. SYN: tunica muscularis pelvis renalis [TA].
- muscular l. of seminal gland [TA] middle l. (between outer connective tissue and inner mucosa) of the seminal gland wall, composed of outer longitudinal and inner circular layers of smooth muscle. SYN: tunica muscularis glandulae vesiculosae [TA].
- muscular l. of small intestine [TA] muscular l. of the wall of the small intestine. SYN: tunica muscularis intestini tenuis [TA], muscular coat of small intestine.
- muscular l. of spongy (male) urethra [TA] relatively sparse l. of mostly longitudinally disposed smooth (involuntary) muscle fibers between the mucosa and the surrounding erectile tissue of the corpus spongiosum penis. SYN: tunica muscularis partis spongiosae urethrae masculinae [TA], muscular coat of spongy part of male urethra.
- muscular l. of stomach [TA] muscular tunic of the stomach, consisting of smooth muscles arranged in three fairly well-defined layers: an outer longitudinal l., continuous with that of the esophagus but dividing at the cardia into two bands which run along the greater and lesser curvatures, leaving the middle areas of the anterior and posterior walls devoid of longitudinal fibers, and then coalescing in the pyloric region into a complete l. which is continuous with the longitudinal coat of the duodenum. The middle circular l. is most complete and strongest, continuous with the circular l. of the esophagus at the cardia; it thickens progressively toward the pylorus, ultimately forming the muscular ring of the pyloric sphincter. The inner, oblique l. is unique to the stomach and is most strongly developed in the fundic region and absent along the lesser curvature. This absence contributes to the formation of the “gastric canal.” SYN: tunica muscularis gastrica [TA], muscular coat of stomach, tunica muscularis ventriculi.
- muscular l. of trachea [TA] muscular l. of the tracheal wall. SYN: tunica muscularis tracheae [TA], muscular coat of trachea.
- muscular l. of ureter [TA] muscular l. of the ureteric wall. SYN: tunica muscularis ureteris [TA], muscular coat of ureter.
- muscular l. of urinary bladder [TA] muscular l. of the wall of the urinary bladder. SYN: tunica muscularis vesicae urinariae [TA], muscular coat of urinary bladder.
- muscular l. of uterine tube [TA] muscular l. of the wall of the uterine tube. SYN: tunica muscularis tubae uterinae [TA], muscular coat of uterine tube.
- muscular l. of vagina [TA] muscular l. of the vaginal wall. SYN: tunica muscularis vaginae [TA], muscular coat of vagina.
- l. of nerve fibers [TA] the l. of the retina composed of the axonal processes of the ganglion cells; these processes converge to form the optic nerve. SYN: stratum neurofibrarum [TA].
- neuroepithelial l. of retina the outermost l. of the cerebral l. of retina, composed of the primary receptor cells of the retina; this area consists of two layers: 1) a l. of inner and outer segments [TA] made up of the rods and cones, the photosensitive processes of the receptor cells, and 2) the outer nuclear l. [TA] containing the cell bodies of these cells; the outer limiting membrane (outer limiting l. [TA]) forms a perforated supporting plate between the two sublayers; the name refers to the fact that the retinal receptor cells are a specialized form of (epithelial) ependyma cell and thus, in a sense, are comparable to the neuroepithelial cells ( e.g., hair cells) of other sense organs. SYN: external nuclear l. of retina, stratum neuroepitheliale retinae.
- nuclear layers of retina the outer nuclear l., l. 4, of the retina, neuroepithelial l. of retina, and the inner l., l. 6, of the retina, ganglionic l. of retina. SYN: strata nuclearia externa et interna retinae.
- optic l. [TA] 1. a l. of white matter interspersed with nerve-cell bodies, immediately below the superficial gray l. of the superior colliculus, composed of myelinated fibers originating in the retina and striate cortex; 2. a rarely used term to describe the inner l. of the retina, consisting of the fibers originating from the cells of the ganglionic l. of the retina; in their further course these fibers combine to form the optic nerve. SYN: stratum opticum [TA].
- oriens l. [TA] See layers of hippocampus. SYN: stratum oriens [TA].
- osteogenetic l. the inner bone-forming l. of the periosteum.
- outer limiting l. [TA] the membranelike structure located immediately internal to the l. of inner and outer segments; made up of processes of the neuroglial cells of the retina (Müller cells); penetrated by the portion of the rods and cones located between the inner and outer segments and the cell body. SYN: stratum limitans externum [TA].
- outer nuclear l. [TA] the l. of the retina containing the cell bodies of the rods and cones. SYN: stratum nucleare externum [TA].
- outer plexiform l. [TA] the l. of the retina composed of the processes of rods and cones, horizontal cells, and bipolar cells; a l. containing synaptic contacts. SYN: stratum plexiforme externum [TA].
- palisade l. SYN: stratum basale epidermidis.
- papillary l. SYN: stratum papillare corii.
- parietal l. [TA] the outer l. 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 l. of the enveloping sac; an actual or potential space is enclosed by the two continuous layers, intervening between parietal and visceral layers. The parietal l. is usually the more substantial l.. SYN: lamina parietalis [TA].
- parietal l. of serous pericardium [TA] the outer part of the serous pericardium suported by the fibrous pericardium. SYN: lamina parietalis pericardii serosi [TA].
- parietal l. of tunica vaginalis of testis [TA] the outer part of the tunica vaginalis testis supported by the internal spermatic fascia. SYN: lamina parietalis tunicae vaginalis testis [TA].
- pigmented l. of retina [TA] the outer l. of the retina, consisting of pigmented epithelium. SYN: ectoretina, stratum pigmenti bulbi, stratum pigmenti retinae, tapetum nigrum, tapetum oculi.
- plasma l. SYN: still l..
- plexiform layers of retina layers of the retina where synapses occur; in the external l., processes of rods and cones synapse with bipolar neuron dendrites; in the internal l., axon terminals of bipolar cells synapse with ganglion cell dendrites. See retina. SYN: stratum plexiforme internum [TA], stratum plexiforme externum.
- posterior l. of rectus sheath [TA] the portion of the sheath of the rectus abdominis muscle that lies posterior to the muscle covering only its upper two-thirds; it is formed by contributions from the aponeuroses of the internal oblique and transversus abdominis muscles; its free inferior margin forms the arcuate line; it is deficient below this, the posterior aspect of the muscle being covered only by transversalis fascia and peritoneum. SYN: lamina posterior vaginae musculi recti abdominis [TA].
- pretracheal l. of cervical fascia [TA] the l. of fascia investing the infrahyoid muscles and contributing to the formation of the carotid sheath. SYN: lamina pretrachealis fasciae cervicalis [TA], middle cervical fascia, Porter fascia, pretracheal fascia.
- prevertebral l. of cervical fascia [TA] the part of the cervical fascia that covers the bodies of the cervical vertebrae and the muscles attaching to them and to the anterior parts of their transverse processes. SYN: lamina prevertebralis fasciae cervicalis [TA], prevertebral fascia.
- prickle cell l. SYN: stratum spinosum epidermidis.
- Purkinje cell l. the l. of large neuron cell bodies located at the interface of molecular and granular layers in the cerebellar cortex; dendrites of these cells fan outward into the molecular l. in a plane transverse to the folium. SYN: stratum purkinjense corticis cerebelli [TA], ganglionic l. of cerebellar cortex, l. of piriform neurons, Purkinje cells, Purkinje corpuscles.
- radiant l. [TA] See layers of hippocampus. SYN: stratum radiatum [TA].
- Rauber l. 1. the thinned-out trophoblastic membrane over the embryonic disk in developing carnivores and ungulates; 2. outermost cell l. which helps form the blastodisk; called blastodermic or primitive ectoderm.
- reticular l. of corium SYN: stratum reticulare corii.
- l. of rods and cones the l. of the retina next to the pigment l. and containing the visual receptors. SEE ALSO: retina, neuroepithelial l. of retina. SYN: bacillary l..
- sluggish l. SYN: still l..
- somatic l. the external l. of the lateral mesoderm of the embryo, lying adjacent to the ectoderm and together with it constituting the somatopleure.
- spinous l. SYN: stratum spinosum epidermidis.
- splanchnic l. the internal l. of the lateral mesoderm, lying adjacent to the endoderm and together with it forming the splanchnopleure.
- spongy l. of female urethra [TA] inappropriate reference to the lamina propria of the mucous membrane of the female urethra, characterized by numerous, thin-walled veins that have in the past been falsely compared with erectile tissue. SYN: tunica spongiosa urethrae femininae [TA].
- spongy l. of vagina [TA] inappropriate collective reference to the abundant venous plexuses of the vagina, occurring within the mucosal and muscular layers (giving the rugae somewhat the character of erectile tissue) as well as in the adventitia (the laterally placed vaginal venous plexuses), falsely suggesting a discrete l. of erectile tissue. SYN: tunica spongiosa vaginae [TA].
- still l. the l. of the bloodstream in the capillary vessels, next to the wall of the vessel, that flows slowly and transports the white blood cells along the l. wall, while in the center the flow is rapid and transports the red blood cells. SYN: plasma l., Poiseuille space, sluggish l..
- subendocardial l. the loose connective tissue l. that joins the endocardium and myocardium; in the ventricles, it contains branches of the conducting system of the heart.
- subendothelial l. the thin l. of connective tissue lying between the endothelium and elastic lamina in the intima of blood vessel s.
- subserous l. subserosa.
- superficial l. [TA] in a stratified structure, the outermost or topmost of the strata; the stratum nearest the surface. See superficial l. of deep cervical fascia, superficial l. of the levator palpebrae superioris, superficial l. of temporal fascia. SYN: lamina superficialis [TA], superficial lamina.
- superficial l. of the levator palpebrae superioris [TA] the superficial fibers of the levator muscle of the superior eyelid which are inserted into the skin of the superior eyelid. SYN: lamina superficialis musculi levatoris palpebrae superioris.
- superficial l. of temporal fascia [TA] the superficial part of the temporal fascia attaching to the lateral surface of the zygomatic arch. SYN: lamina superficialis fasciae temporalis [TA].
- suprachoroid l.
- Tomes granular l. a thin l. of dentin adjacent to the cementum, appearing granular in ground sections; the granules are small uncalcified spaces.
- vascular l. of eyeball [TA] the vascular, pigmentary, or middle coat of the eye, comprising the choroid, ciliary body, and iris. SYN: tunica vasculosa bulbi [TA], Haller tunica vasculosa, tunica vasculosa oculi, uvea, uveal tract, vascular tunic of eye.
- vascular l. of testis [TA] innermost of three coats (with tunicae vaginalis and albuginea) investing the testis consisting of a vascular plexus in a delicate loose connective tissue matrix that covers the internal aspect of the tunica albuginea and extends deeply, covering the septa and therefore surrounding the lobules of the testis. SYN: tunica vasculosa testis [TA].
- ventricular l. SYN: ependymal l..
- visceral l. [TA] the inner l. of an enveloping sac or bursa which lines the outer surface of the enveloped structure, as opposed to the parietal l. which lines the walls of the occupied space or cavity. The visceral l. is usually thin, delicate and not apparent as being separate, but rather appears to be the outer surface of the structure itself. SEE ALSO: serosa. SYN: lamina visceralis [TA].
- visceral l. of serous pericardium [TA] the inner part of the serous pericardium applied directly on the heart. SYN: epicardium, lamina visceralis pericardii.
- visceral l. of tunica vaginalis of testis [TA] the inner part of the tunica vaginalis testis applied directly to the testis and epididymis. SYN: lamina visceralis tunicae vaginalis testis [TA].
- Waldeyer zonal l. SYN: dorsolateral fasciculus.
- Weil basal l. the l. beneath the odontoblasts of the tooth; it contains reticular fibers but few if any cells. SYN: Weil basal zone.
- zonular l. 1. a thin l. of white substance covering the upper surface of the thalamus and forming part of the floor of the body of the lateral ventricle; 2. a l. of white substance on the surface of the superior colliculus. SYN: stratum zonale [TA].
* * *
lay·er 'lā-ər, 'le(-ə)r n
1) one thickness, course, or fold laid or lying over or under another
layer vb
* * *
lay·er (laґər) 1. a stratum or lamina; a sheetlike mass of substance of nearly uniform thickness, several of which may be superimposed, one above another. 2. a female bird of the age when it is laying eggs.For descriptions of specific anatomic structures not listed here, see under lamina and stratum.
Medical dictionary. 2011.