| Sydney line | A variation of the proximal transverse palmar flexion crease that reaches the ulnar side of the palm; associated with acute lymphocytic anaemia in early childhood, rubella embryopathy, and Down's syndrome. Synonym: Sydney line. (05 Mar 2000) |
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| sylvian line | The line of the posterior limb of the lateral sulcus (sylvian fissure) of the cerebral cortex. (05 Mar 2000) |
| dentate line | The line between the simple columnar epithelium of the rectum and the stratified epithelium of the anal canal. Synonym: linea anocutanea, anocutaneous line, dentate line. (05 Mar 2000) |
| Douglas' line | A crescentic line, not always clearly defined, which marks the lower limit of the posterior layer of the sheath of the rectus abdominis muscle. Synonym: linea arcuata vaginae musculi recti abdominis, Douglas' line, linea saemicircularis, saemicircular line. (05 Mar 2000) |
| drift line | An accumulation of water-carried debris along a contour or at the base of vegetation that provides direct evidence of prior inundation and often indicates the directional flow of flood waters. (09 Oct 1997) |
| iliopectineal line | An oblique ridge on the inner surface of the ilium and continued on the pubis, which forms the lower boundary of the iliac fossa; it separates the true from the false pelvis. Synonym: iliopectineal line, terminal line. (05 Mar 2000) |
| inferior nuchal line | A ridge that extends laterally from the external occipital crest toward the jugular process of the occipital bone. Synonym: linea nuchae inferior. (05 Mar 2000) |
| inferior temporal line | The lower of two curved lines on the parietal bone; it marks the outer limit of attachment of the temporalis muscle. Synonym: linea temporalis inferior, temporal ridge. (05 Mar 2000) |
| infracostal line | A horizontal plane passing through the inferior limits of the costal margin, i.e., the tenth costal cartilages; it marks the boundary between the hypochondriac and epigastric regions superiorly and the lateral and umbilical regions inferiorly. Synonym: planum subcostale, infracostal line. (05 Mar 2000) |
| intercondylar line of femur | A faint transverse ridge separating the floor of the intercondylar fossa from the popliteal surface of the femur; it affords attachment to the posterior portion of the articular capsule of the knee. Synonym: linea intercondylaris femoris. (05 Mar 2000) |
| intermediate line of iliac crest | The line on the crest of the ilium between the outer and inner lips, for origin of internal oblique muscle. Synonym: linea intermedia cristae iliacae. (05 Mar 2000) |
| internal oblique line | A ridge on the inner surface of the mandible running from a point inferior to the mental spine upward and backward to the ramus behind the last molar tooth; it gives attachment to the mylohyoid muscle and the lowermost part of the superior constrictor of the pharynx. Synonym: linea mylohyoidea, internal oblique line, mylohyoid ridge. (05 Mar 2000) |
| interspinal line | Line passing through both anterior superior iliac spines indicating the interspinal plane. Synonym: linea interspinalis. (05 Mar 2000) |
| intertrochanteric line | A rough line that separates the neck and shaft of the femur anteriorly; it passes downward and medially from the greater trochanter to the lesser trochanter and continues into the medial lip of the linea aspera. Synonym: linea intertrochanterica, linea spiralis, spiral line. (05 Mar 2000) |
| intertubercular line | Line passing through tubercles of both iliac crests, indicating the intertubercular plane. Synonym: linea intertubercularis. (05 Mar 2000) |