CHAPTER II.

THE MUSCLES OF THE HAND AND OF THE FINGERS.

Leaving aside the vessels and nerves unconnected with our subject, we may describe the hand as being composed of three classes of organs, 1. bones with joints, 2. ligaments, 3. muscles.

1. BONES WITH JOINTS.

The hand is subdivided into five separate limbs (fingers), lying one at the side of the other, and being, at the lower end, firmly joined together into one whole. Each of these five limbs (fingers) is composed of a row of bones, having the nature of long bones. The first of these bones, next to the lower arm, is called the metacarpal or middle-hand bone (Fig. 1 _a_); the others are called finger-joints. The thumb has only two finger-joints, the other fingers three each. The _fourth and fifth fingers are the weakest of all_.

The union of the five fingers into one whole is effected by means of the extremities of the middle-hand bones, commonly known as knuckles, which are turned towards the forearm, being connected with one another by _very tight transversal ligaments_ (Fig 2 _aa_ and Fig. 3 _bb_), and being thus connected, are again fixed to a row of four roundish bones, joined to one another in the same manner (Fig. 1 _b_). Thus, the five middle-hand bones and the four bones of the upper wrist form one firm structure. In this structure the middle-hand bone of the thumb and of the little finger can be more easily moved than the others.

On account of this moveability of the two extreme middle-hand bones, it is possible to move the two edges of the hand close to one another, whereby the cavity of the hand assumes the shape of a groove.

The structure here described (the hand, in the narrower sense of the word) is joined to the lower arm by means of three muscles, the posterior row of the bones of the wrist (Fig. 1 _c_). The movement between these bones and the hand is hardly anything but a hinge-movement; that between them and the lower arm, however, is a movement in almost all directions. The bending and stretching of the hand is, therefore, produced with the participation of both joints, the side movement of the hand, however, almost exclusively by the joint situated between the posterior row of the bones of the wrist and the lower arm.[2]

2. LIGAMENTS.

All the finger-joints are provided with capsules, which are woven out of strong _transversal_ fibres (Fig. 3 _aa_). The bones of the wrist are connected between themselves and with the bones of the middle-hand by tight transversal and longitudinal ligaments, as seen in Fig. 2 _aa_, _bb_. Lastly, the _two ends of the middle-hand bones, or knuckles, are connected with one another and with the first joints of the fingers by a separate strong, transversal ligament_ (Fig. 2 _aa_, Fig. 3 _bb_).

3. THE MUSCLES OF THE HAND consist

1. Of muscles (four in number) rising from the lower arm and bending the wrist up and down, right and left (Fig. 3 _c_, _d_, _e_).

2. Of muscles of the fingers. These are subdivided into—

_a._ Extensors of the fingers, being situated in the back part of the hand and rising from the bones of the lower arm (Fig. 4 _a_).

_b._ Benders of the fingers. Two muscles, the one for the second joints of the fingers (Fig. 3 _d_), the other for the first joints of the fingers and the joints of the nails (Fig. 3 _e_) also rising from the bones of the lower arm.