(From extendo, to stretch out). An extender. This name is given to several muscles.
Extensor Carpi radialis. This muscle takes Its origin from the rising line of the os humeri, that runs towards the outer condyle, and from the same condyle it runs close to the radius; and passing through a groove where it is bound down, it divides into two tendons: the muscle in this part is sometimes called bicornis. One of these tendons is inserted into the basis of the first, and the other into that of the second, metacarpal bone. This muscle is occasionally called the radiaeus exter-nus; sometimes extensor carpi exterior, and geminus; by Winslow ulnaris externus.
Extensor carpi ulnaris, is sometimes called extensor carpi interior. It rises from the outer condyle of the os humeri, and then originates from the edge of the ulna; its tendon passes in a groove behind the styloid process of the ulna; it proceeds and is inserted into the inside of the basis of the metacarpal bone of the little finger.
The extensors, whether belonging to the fingers or carpus, arise from the outward extuberance of the os humeri: and their antagonists, the flexors, from the internal protuberance of the same bone, as well as from the upper and external part of the ulna next to the anconaeus.
Extensor digitorum communis is also called digitorum tensor. It partly rises from the outer condyle of the os humeri, and partly from the outer edge of the ulna; passes behind the lower extremity of the radius, where there is a groove for its lodgement, and forms four tendons: that for the little finger differs in its passage from the others; the three last communicate, and are inserted into the second bone, and partly into the last of the respective fingers, that is, the third, middle, and fore fingers.
Extensor digitorum bre'.vis is also called pedi-cus. It rises from the anterior part of the os calcis, runs across the instep, and divides commonly into four tendons, sometimes only into three, which are inserted into the three toes next to the greater one, or into all the four.
Extensor digitorum longus; enemodactylaeus; by Dr. Hunter extensor longus digitorum pedis. It rises from the upper part of the tibia and fibula, and the interosseous ligament; its tendon passes under the annular ligament, and then divides into five, four of which are inserted into the second and third phalanges of the toes, and the fifth goes to the basis of the metatarsal bone. The last Winslow reckons a distinct muscle, calling it peronaeus brevis.
Extensor Indicis is also called indicator, and extensor indicis proprius. It rises with the extensor digitorum communis, lies between the ulna and radius, runs close to the interosseous ligament, passes over the back of the hand, and is inserted into the posterior part of the index.
Extensor longus rises from the inferior costa of the scapula; and the
Extensor brevis rises from the outer spine of the humerus; they then make one tendon with the bra-chiaeus internus.
Externus minimi digiti, is also called auricularis. It rises partly tendinous at the extremity of the external apophysis of the os humeri, and partly fleshy from the superior part of the ulna, and becomes tendinous as it passes under the annular ligament at the carpus, where it is divided into two, and sometimes into three, tendons, which are united into one at its insertion into the superior part of the third bone of the little finger.
Extensor primi internodii pollicis rises high up from the radius, ulna, and interosseous ligament: it turns round the radius, runs across the carpus, and is inserted into the trapezium, and the first bone of the thumb.
Exiknsor secundi internodii pollicis rises from the radius, and the interosseous ligament describes the same course as the preceding, and is inserted the second bone of the thumb.
Extensor tertii internodii pollicis rises from the back part of the ulna, near the middle, and from the interrosseous ligament; then goes obliquely across the carpus to the third bone of the thumb. Its action not only extends, but also brings the thumb backward, so that the end of the thumb can sometimes be brought to the wrist.
Extensor pollicis longus rises from the middle and fore part of the fibula, and the interrosseous ligament, and passes over the instep to be inserted into the last bone of the great toe.
Extensor pollicis brevis is only a slip from the extensors of the toes, inserted into the first bone,