| musculus incisurae helicis | An occasional muscle on the cranial surface of the auricle spanning the antitragohelicine fissure. Synonym: musculus incisurae helicis, musculus intertragicus. (05 Mar 2000) |
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| musculus infracostalis | <anatomy> One of a number of inconstant muscles of the posterolateral thoracic wall having the same direction as the internal intercostal muscles but extending across (deep to) one or more ribs. Synonym: musculus subcostalis, musculus infracostalis. (05 Mar 2000) |
| musculus infraspinatus | <anatomy, muscle> Origin, infraspinous fossa of scapula; insertion, middle facet of greater tubercle of humerus; action, extends arm and rotates it laterally; nerve supply, suprascapular (from fifth to sixth cervical spinal nerves). Synonym: musculus infraspinatus. (05 Mar 2000) |
| musculus intercostales externi | Each arises from lower border of one rib and pass obliquely downward and forward to be inserted into the upper border of rib below; action, contract during inspiration, also maintain tension in the intercostal spaces to resist mediolateral movement; nerve supply, intercostal. Synonym: musculus intercostales externi. (05 Mar 2000) |
| musculus intercostalis internus | <anatomy> Each arises from lower border of rib and passes obliquely downward and backward to be inserted into upper border of rib below; action, contract during expiration, also maintain tension in the intercostal spaces to resist mediolateral movement; nerve supply, intercostal. Synonym: musculus intercostalis internus. (05 Mar 2000) |
| musculus intercostalis intimus | <anatomy> A layer parallel to and essentially part of the internal intercostal muscle but separated from it by the intercostal vessels and nerves.internal intercostal muscle for attachment, action and nerve supply. Synonym: musculus intercostalis intimus. (05 Mar 2000) |
| musculus interosseus palmaris | <anatomy> Three muscles in the hand; origin, first: ulnar side of second metacarpal; second and third: radial sides of fourth and fifth metacarpals; insertion, first: into ulnar side of index; second and third: into radial sides of ring and little fingers; action, adducts fingers toward axis of middle finger; nerve supply, ulnar. See: flexor pollicis brevis muscle. Synonym: musculus interosseus palmaris, musculus interosseus volaris. (05 Mar 2000) |
| musculus interosseus plantaris | <anatomy> Three intrinsic muscles of foot; origin, the medial side of the third, fourth, and fifth metatarsal bones; insertion, corresponding side of proximal phalanx of the same toes; action, adducts three lateral toes; nerve supply, lateral plantar. Synonym: musculus interosseus plantaris. (05 Mar 2000) |
| musculus interosseus volaris | <anatomy> Three muscles in the hand; origin, first: ulnar side of second metacarpal; second and third: radial sides of fourth and fifth metacarpals; insertion, first: into ulnar side of index; second and third: into radial sides of ring and little fingers; action, adducts fingers toward axis of middle finger; nerve supply, ulnar. See: flexor pollicis brevis muscle. Synonym: musculus interosseus palmaris, musculus interosseus volaris. (05 Mar 2000) |
| musculus interspinalis cervicis | Origin, tubercle of spinous process of cervical vertebra; insertion, tubercle of spinous process of next superior vertebra; action, extends the neck; nerve supply, dorsal rami of cervical nerves. Synonym: musculus interspinalis cervicis, cervical interspinal muscle. (05 Mar 2000) |
| musculus interspinalis lumborum | Origin, superior margin of lumbar spinous process; insertion, inferior margin of next superior spinous process; action, extends lumbar vertebrae; nerve supply, dorsal primary rami of lumbar spinal nerves. Synonym: musculus interspinalis lumborum, lumbar interspinal muscle. (05 Mar 2000) |
| musculus interspinalis thoracis | Often poorly developed or absent muscles between spinous process of thoracic vertebrae; action, extends thoracic vertebrae; nerve supply, dorsal primary rami of thoracic nerves. Synonym: musculus interspinalis thoracis, thoracic interspinal muscle. (05 Mar 2000) |
| musculus intertragicus | An occasional muscle on the cranial surface of the auricle spanning the antitragohelicine fissure. Synonym: musculus incisurae helicis, musculus intertragicus. (05 Mar 2000) |
| musculus ischiocavernosus | <anatomy, muscle> Origin, ramus of ischium; insertion, corpus cavernosum penis (or clitoridis); action, compresses the crus of the penis (or clitoris) forcing blood in its sinuses into the distal part of the corpus cavernosum; nerve supply, perineal. Synonym: musculus ischiocavernosus, musculus erector clitoridis, musculus erector penis. (05 Mar 2000) |
| musculus ischiococcygeus | <anatomy, muscle> Origin, spine of ischium and sacrospinous ligament; insertion, sides of lower part of sacrum and upper part of coccyx; action, assists in support of pelvic floor, especially when intra-abdominal pressures increase; nerve supply, third and fourth sacral. Synonym: musculus coccygeus, coccygeal muscle, musculus ischiococcygeus. (05 Mar 2000) |