Rclations.—It is covered by the two last muscles ; its posterior surface is applied to the fifth metacarpal bone, the corresponding inter osseous, and the tendon of the flexor sublimis going to the little finger.
It carries the fifth metacarpal bone forwards and outwards, thereby augmenting the cavity of the hand, and in a measure opposing the little finger to the thumb, but the articulation of the metacarpal bone, with the os unciforme allows of so very little rotatory motion, that it is rather a motion of adduction and flexion than of opposition.
c. Muscles of the middle palmar region.— In the middle palmar region we have seven muscles, four connected to the tendons of the flexor profundus, the lumbricales, so called from their resemblance to earth-worms; and three deeper-seated muscles, the palmar inter ossei occupying a part of the second, third, and fourth interosseous spaces between the meta carpal bones, the remaining part of those spaces being filled up by muscles ; we shall presently examine the dorsal interossei.
1. Lumbricalcs (flcctentcs primum intcrno dingy Spig.) are four slender, elongated, fusi form, fleshy bundles, attached to the tendons of the flexor profundus, just after it escapes from under the annular ligament, distinguished into first, second, &e. from without inwards. The first arises from the fore and outer part of the flexor profundus tendon belonging to the index finger, sometimes also from the accompanying tendon of the flexor sublimis ; the recand lum bricalis arises from the radial side of the tendon of the same muscle destined to the middle finger ; the third and fourth are double penni form arising from the opposed surfaces of the three internal tendons of the same muscle; from these attachments they proceed, the two middle vertically downwards, the outer out wards, the inner inwards, towards the outer side of the metacarpo-phalangeal articulations of the fingers, where they end in flat broad tendons, which are inserted into the outer border of the common extensor tendon, in common with the tendons of the correspond ing interossei with which they are confused ; they assist in completing the sheath which the extensor tendons form for the back of the fingers.
Relationt—Their anterior surface is covered by the tendons of the flexor subliints, by the palmar aponeurosis, and collateral vessels and nerves of the fingers. Their posterior surface lies upon the interossei, the inferior transverse metacarpal ligament, and the phalanges.
Use.—They assist in the flexion of the fingers upon the metacarpus, at the same time drawing them outwards, they steady the extensor ten dons, keeping them applied to the phalanges.
The interossei, of which there are seven in all, are small muscles situated between the meta carpal bones, to which they are attached supe riorly, their inferior attachment being to the sides of the first phalanges and the extensor eominunis tendons; there are three on the pal mar aspect, which are simple, and four on the dorsal aspect of the hand, which are bifid mus cles; there are two to each interosseous space, excepting the first, which has only one : we shall first examine the palmar interossei.
2. Interossei interne digitorummanus,(meta rarpo-phalangiens lateraur palmaires, Chauss.) Short, prismatic, and triangular; they arise, the first, or posterior indices, from the root and inner side of the metacarpal bone of the forefinger; the second, or prior armatures, from the root and outer side of the metacarpal bone of the ring finger ; the third, or interosseus uarieulares, from the root and outer side of the metacarpal bone of the little finger. They extend along the metacarpal bones, to which they are attach ed, and are inserted by short tendons; the second and third in common with those of the lumbrieales, into the outer and upper, and the first into the inner and upper part of the corre sponding first phalanges and side of the exten sor tendons.
Relations.—Anteriorly they are covered by the deep flexor tendons and palmar muscles; posteriorly they correspond to the dorsal inter ossei, which are also connected with them along their unattached margin.