CHAP. IV THE RIDGES AND THEIR USES 5 5
that which runs over the ball of the thumb and adjacent parts of the palm. It is bounded by the line a which starts from the middle of the palm close to the wrist, and sweeps thence round the ball of the thumb to the edge of the palm on the side of the thumb, which it reaches about half an inch, more or less, below the base of the fore-finger. The system AB is bounded towards the thumb by the above line a, and towards the little finger by the line b ; the latter starts from about the middle of the littlefinger side of the palm, and emerges on the opposite side just below the fore-finger. Consequently, every ridge that wholly crosses the palm is found in AB. The system BC is bounded thumbwards by the line b, until that line arrives at a point immediately below the axis of the fore-finger ; there the boundary of BC leaves the line b, and skirts the base of the forefinger until it reaches the interval which separates the fore and middle fingers. The upper boundary of BC is the line c, which leaves the little-finger side of the palm at a small distance below the base of the little finger, and terminates between the fore and middle fingers. Other systems are found between c and the middle, ring, and little fingers ; they are somewhat more variable than those just described, as will be seen by comparing the five different palms shown in Fig. 6.
An interesting example of the interpolation of a small and independent system occurs frequently in the middle of one or other of the systems AB or BC, at the place where the space covered by the systems
