(līn)

[L. linea, string, thread]

1. A narrow straight mark.
2. A boundary, edge, or outline.
3. A wrinkle.
4. An imaginary anatomical line used as a standard of reference.
5. A catheter attached to a patient, e.g., an intravenous line or an arterial line.

abdominal line

Any of the standard imaginary surface lines delineating abdominal regions.
SEE: abdominal regions

absorption line

A black line in the continuous spectrum of light passing through an absorbing medium.

ala-tragus line

An imaginary line that extends from the ala of the nose to the tragus of the ear. The line is an estimated point of entry for intraoral dental radiographs of the maxilla and is also used in denture prosthodontics.

arcuate line

1. The lower edge of the iliac fossa of the ilium. The arcuate line is a continuation of the pectineal line of the pubis, and it continues up and back along the ilium to merge with the edge of the sacral ala and then the sacral promontory. The continuous bony ridge, of which the arcuate line is one segment, encircles the pelvic inlet and is called the pelvic brim.
2. On the internal surface of the anterior abdominal wall, below the level of the umbilicus, the inferior edge of the posterior layer of the rectus sheath. At this level, the inferior epigastric vessels enter the sheath and run along the underside of the rectus abdominis muscles.

Arlt line

SEE: Arlt line

arterial line

A hemodynamic monitoring system consisting of a catheter in an artery connected to pressure tubing, a transducer, and an electronic monitor. It is used to measure systemic blood pressure and to provide ease of access for the drawing of blood (as in intensive care, when regular monitoring of blood gases is necessary).

auriculobregmatic line

The line from the auricular point to the bregma.

axial line

A line running in the main axis of the body or a body part, such as a limb. For example, the axial line of the hand runs longitudinally through the middle digit; the axial line of the foot runs longitudinally through the second digit.

axillary line

Any of the imaginary lines that extend in parallel down the side of the body from the axilla. These lines are the anterior axillary line, the midaxillary line, and the posterior axillary line.

base line

An imaginary cephalometric line from the infraorbital ridge through the middle of the external auditory meatus to midline of occiput.
SEE: baseline

basiobregmatic line

The line from the basion to the bregma.

Baudelocque line

SEE: Baudelocque, Jean-Louis

Beau line

SEE: Beau line

biauricular line

A line over the vertex from one auditory meatus to the other.

blue line

SEE: Lead line.

Burton line

SEE: Burton line

canthomeatal line

An imaginary cephalometric line extending from the lateral canthus of the eye to the center of the external auditory meatus.

cement line

The edge of a secondary (new) osteon. It contains glycoproteins and proteoglycans and has little or no collagen.

central line

A venous access device inserted into and kept in the vena cava, innominate, or subclavian veins. It is used to infuse fluids and medicines or for gaining access to the heart to measure pressures in the venous circulation. Keeping the line open permits later venous access when the veins might be collapsed and difficult to enter.
SEE: central venous catheter

central intravenous line

SEE: central venous catheter; SEE: central line

cervical line

1. A line of junction of cementum and enamel of a tooth.
2. A line on the neck of the tooth where the gum is attached.

cleavage lines

SEE: Langer line.

costoarticular line

The line from sternoclavicular joint to a point on the 11th rib.

costoclavicular line

The line midway between the nipple and the border of the sternum.

line of demarcation

demarcation line The dividing line between healthy and diseased tissue.

dentate line

On the luminal wall, the transition zone between the anal canal and the rectum. Inside the anal canal, the anal valves are located along the pectinate line; outside the anal canal, the superficial portion of the external anal sphincter is located at the pectinate line. The pectinate line marks where, in the embryo, two separate epithelia (the endoderm of the developing hindgut and the ectoderm of the invaginating proctodeum) meet and fuse.
SYN: SEE: pectinate line

line of Douglas

Douglas line
SEE: Douglas, James

ectental line

The junction in the gastrula of the endoderm and ectoderm.

epiphyseal line

A line marking the junction of the epiphysis and diaphysis of a long bone. It is the remnant of the epiphyseal disk.

Feiss line

SEE: Feiss line

line of fixation

fixation lineSEE: Visual line

frown line

A permanent skin fold or wrinkle between the eyebrows or near the corners of the mouth that develops as a result of repeated use of underlying muscles and aging.

gingival line

SEE: Gumline.

glabelloalveolar line

An imaginary line through the glabella on the frontal bone and the alveolar process of the maxilla.

glabellomeatal line

An imaginary line that extends from the glabella to the center of the external auditory meatus and is used for radiographical positioning of the skull.

gluteal line

Any of three lines (the posterior, the anterior, or the inferior gluteal) that are bony ridges on the posterior (exterior) surface of the ilium parallel to the iliac crest. The posterior gluteal line runs along the outer edge of the iliac crest and marks the upper edge of the origin of the gluteus medius muscle. The anterior gluteal line has the same contour as the iliac crest but runs a few centimeters lower and marks the upper edge of origin of the gluteus minimus muscle. The inferior gluteal line has a contour similar to, but fainter than, the other gluteal lines, it runs a few centimeters above the acetabulum, and it marks the lower edge of the origin of the gluteus minimus muscle on the ilium.

gum line

SEE: gumline

Hilton line

SEE: Hilton, John

iliopectineal line

The segment of the pelvic brim from the pubic symphysis to the sacrum, including the pubic crest, the pectineal line, and the arcuate line.

incremental line

Any of the lines seen in a microscopic section of tooth enamel. They mark the sequential layers of added enamel, similar to the growth lines in a tree.

incremental line of Retzius

SEE: Retzius, Magnus Gustaf

incremental line of von Ebner

Very light lines in the dentin of a tooth that represent the boundary between the layers of dentin produced daily.

inferior nuchal line

On the posterior outer surface of the occipital bone, a ridge extending laterally from either side of the greater occipital crest 1 to 2 cm below the greater external occipital protuberance and curving slightly upward at its end.

infraorbitomeatal line

ABBR: IOML An imaginary line from the inferior orbital margin to the external auditory meatus, used for radiographical positioning of the skull.

interauricular line

An imaginary cephalometric line passing through the left and right external auditory meatus.

intercondylar line

The transverse ridge joining condyles of the femur above the intercondyloid fossa.

intermediate line of ilium

The ridge on the crest of the ilium between the inner and outer lips.

interpupillary line

ABBR: IPL An imaginary horizontal line drawn between the centers of the pupils of the eyes. The length of the line is the interpupillary distance.

intertrochanteric line

A roughened circumferential ridge at the base of the neck of the femur interconnecting the greater and lesser trochanters.

intertuberal line

The line joining the inner borders of the ischial tuberosities below the lesser sciatic notch.

intraperiod line

SEE: major dense line

Langer lines

SEE: Langer lines

lateral canthal line

Skin folds or wrinkles that form at the temporal sides of the eyes. Also technically known as lateral canthal rhytids. Colloquially known as “crow’s feet.”

lateral supracondylar line

Either of two ridges on the posterior surface of the distal end of the femur, formed by diverging lips of the linea aspera. It is one of the proximal attachments of the vastus lateralis muscle of the quadriceps.
SEE: medial supracondylar line

lead line

An irregular dark line in the gingival margin. The line is present in chronic lead poisoning and is caused by the deposition of lead in that portion of the gum.
SYN: SEE: blue line

lip line

The highest or lowest point the lips reach on the teeth or gums during a broad smile.

M line

In high power micrographs of striated muscle, the thin, dark line in the center of the H band of a sarcomere. It contains myomesin (a protein that connects thick (myosin) filaments), C protein, and creatinine kinase.
SYN: SEE: M band; SEE: M disk

magnetic lines of force

The lines indicating the direction of the magnetic force in the space surrounding a magnet or constituting a magnetic field.

major dense line

In electron microscopic images of myelin sheaths, the compacted cytoplasmic side of the Schwann cell membranes, which alternates in multiple layered sheaths with tightly opposed external membrane surfaces called the minor dense line or the intraperiod line.
SYN: SEE: period line
SEE: intraperiod line

mammillary line

An imaginary line through the center of the nipple along the long axis of the breast.

mammary line

SEE: Milk line.

marionette line

The indentation in the facial skin that runs from the corner of each side of the mouth, to the corner of the chin. The line tends to deepen with age. One element of plastic surgery to rejuvenate the face is to eliminate this line with natural or artificial fillers.

medial supracondylar line

Either of two ridges on the posterior surface of the distal end of the femur, formed by diverging lips of the linea aspera.
SEE: lateral supracondylar line

median line

An imaginary vertical line dividing the body (or one of its parts) into a right and a left side.

mentomeatal line

An imaginary line from the mental point of the mandible to the external auditory meatus, used in radiography of the skull.

midclavicular line

An imaginary longitudinal line through the middle of the clavicle, used for describing locations on the trunk. At its top, it passes through the midpoint of the clavicle, and on a male, it runs just medial to the nipple. It crosses the costal margin near the end of the 9th costal cartilage and it extends to the thigh, passing through the fold of the groin halfway between the anterior superior iliac spine and the symphysis pubis. At one point, the milk line (mammary line) intersects the midclavicular line.

milk line

A longitudinal line along each side of the chest and abdomen of mammals marking the location of the mammary ridge of the embryo. Mammary glands and nipples (both normal and supernumerary) develop along the milk line. The milk line and the midclavicular line intersect at one point.
SYN: SEE: mammary line
SEE: mammary ridge

mucogingival line

SEE: Mucogingival junction

mylohyoid line

A ridge on the inner surface of the mandible. It extends from a point beneath the mental spine upward and back to the ramus past the last molar. The mylohyoid muscle and the superior constrictor muscle of the pharynx attach to this ridge.

nasal line

A line from the lower edge of the ala nasi curving to the outer side of the orbicularis oris muscle.

nasobasilar line

A line through the basion and nasion.

neonatal line

A prominent incremental line in the tooth enamel and dentine made partly after birth. The line indicates infant survival for at least a few days after birth.

nuchal line

The inferior or the superior nuchal line.

oblique line of fibula

The medial crest of posteromedial border; a line extending from the medial side of the head and terminating distally at the interosseous crest.

oblique line of mandible

On the outside of the body of the mandible, a ridge continuing from the line of the anterior border of the mandibular ramus. As it passes the region below the first molar, the oblique line curves forward and runs (below the mental foramen) parallel to the lower edge of the mandible; it finally disappears into the mental tubercle. The oblique line marks the attachments of several muscles: the depressor labii inferioris, the depressor anguli oris, and parts of the platysma.

oblique line of radius

The faint ridge on the anterior surface passing inferolaterally from the radial tuberosity.

oblique line of thyroid cartilage

A line running obliquely across the external surface of each of the two laminae of the thyroid cartilage. Three muscles attach to this ridge: the sternothyroid, the thyrohyoid, and the thyropharyngeus portion of the inferior pharyngeal constrictor.

oculozygomatic line

A line appearing between the inner canthus of the eye and the cheek, supposedly indicative of neural disorders.

orbitomeatal line

The imaginary line running through the outer (lateral) canthus of the eye and the ipsilateral external auditory meatus. It is commonly used for radiographic positioning.

line of Owen

Any of the occasional prominent growth lines or bands in the dentin of a tooth. They provide a record of the growth of the coronal or radicular dentin.

parasternal line

The line midway between the midclavicular line and the ipsilateral border of the sternum.

pectinate line

SEE: Dentate line

pectineal line

1. A ridge along the upper edge of the superior ramus of the pubis (pubic bone) extending from the pubic tubercle to the ilium, where it continues as the arcuate line. Together, the pectineal line and the arcuate line form the iliopectineal line, which is a large portion of the pelvic brim.
SYN: SEE: pecten pubis
2. A short, rough ridge on the posterior surface of the femur extending downward from the lesser trochanter to the linea aspera. The pectineus muscle attaches to this ridge.

period line

SEE: Major dense line.

popliteal line of femur

An oblique line on the posterior surface of the femur.

popliteal line of tibia

A line on the posterior surface of the tibia, extending obliquely downward from the fibular facet on the lateral condyle to the medial border of the bone.

pure line

1. The progeny of a single homozygous individual obtained by self-fertilization.
2. The progeny of an individual reproducing asexually by simple fission, or by buds, runners, or stolons.
3. The progeny of two homozygous individuals reproducing sexually.

resting line

A smooth cement line seen in microscopic sections of bone; it marks a place where bone growth stopped temporarily and then resumed.

reversal line

A cement line seen in microscopic sections of bone that shows scallops and irregularities representing earlier bone resorption. Resorption to that point occurred before the process reversed and new bone was formed by apposition.
SEE: Howship lacuna

scapular line

In anatomical descriptions, an imaginary vertical line parallel to the midline and passing through the tip of the inferior angle of the scapula when the ipsilateral arm is hanging at the side of the body.

Schwalbe line

SEE: Schwalbe, Gustav Albert

semilunar line

SEE: linea semilunaris

Shenton line

SEE: Shenton line

sight line

An imaginary line from the center of the pupil to a viewed object.

skin tension line

SEE: Langer line.

soleal line

A roughened diagonal line on the posterior surface of the upper quarter of the tibia. It descends from the back of the tibial tuberosity to the medial edge of the shaft of the tibia. Part of the soleus muscle originates from the soleal line.

spigelian line

SEE: spigelian line

sternal line

An imaginary vertical midline passing through the sternum.

sternomastoid line

A line connecting the midpoint of the heads of the sternocleidomastoid muscle and the mastoid process of the temporal bone.

superior nuchal line

On the posterior outer surface of the occipital bone, a ridge extending laterally from either side of the greater occipital protuberance and curving slightly downward at its end.

supraorbital line

The line across the forehead above the root of the exterior angular process of the frontal bone.

sylvian line

A line on exterior of the cranium, marking direction of the sylvian fissure.

temporal line

Either of two lines, the superior or the inferior temporal. The superior temporal line is an arching ridge along the lateral surface of the skull; it begins as a continuation of the upper posterior border of the zygomatic bone and continues as a broad arch along the frontal and parietal bones, above and roughly parallel to the upper edge of the temporal bone. The inferior temporal line begins with the superior temporal line and separates from its lower edge to form a parallel but tighter and lower arch. The inferior temporal line marks the origin of the temporalis muscle; the superior temporal line marks the attachment of the muscle's fascia.

temporal line of frontal bone

A line from the posterior edge of the zygomatic process of the frontal bone, curving up and back, dividing into the superior and inferior temporal lines.

umbilicopubic line

The portion of median line extending from the umbilicus to the symphysis pubis.

visual line

An imaginary line connecting the fovea of the eye to the object being viewed.
SYN: SEE: line of fixation; SEE: visual axis

warm line

Any means of communication that provides access to consultative or managerial services, typically within several hours or a day.
SEE: hotline

white line

SEE: linea alba

Z line

Regular dark striations visible in high power micrographs of skeletal muscle fibers. Z lines mark the ends of sarcomeres and are the anchors for the sarcomere's actin filaments.
SYN: SEE: Z band
SEE: Z disk

Zöllner lines

Parallel lines, usually three long ones, with a series of short lines drawn at regular intervals across one of the lines at approx. 60°. Similar lines are drawn across the second line at the angle of approx. 120°. Short lines are drawn across the third at the same angle as on the first lines. These lines produce the optical illusion that the long lines are converging or diverging.