reaches a line with that of the metacarpal bone; in another it may be possible to continue the extension until the two bones form an angle with a dorsal opening of 90°. At the first inter-phalangeal joint there is a similar but less extensive variation. The extreme flexion angle is 60° or 70°, and the full extension may be checked as soon as the axes of the two bones are in the same line (frequently a little before this point is reached), or may be carried on 30° beyond. In the distal joint the flexion angle is about 80°, and extension may be checked when the two bones are in the same line, or may be capable of continuation for 40° or more. In the thumb the range of movement at the metacarpo-phalangeal joint varies from 80° to 170°, and at the inter-phalangeal joint from 90° to 120°, in different persons—i.e., the physiological variation in the two articulations is 90° and 30° respectively. The diagram (Fig. 7) may help to render this clear. It is not only in different individuals that such variations are apparent, but the fingers of the same hand and corresponding fingers in opposite hands may differ from each other to a marked degree in range of extension. The super-extension is usually greatest in childhood, and undergoes great diminution as adult life is approached, although in many cases it is persistent; as a rule, however, the limitation is in direct proportion to the strength of the hand, and is hence nearly always greater in the left hand than in the right. These peculiarities are matters of common observation, and popular expressions have ever been coined to represent the extremes in the range of variation. Thus a person who is able to bend his joints backwards to a conspicuous degree is said to be “double-jointed,” and one who cannot extend them beyond the straight line is called “stiff-jointed”; and it is well known that “double-jointedness” and “stiff-jointedness” run in families, and in some cases may be traced through several generations. In the author, for example, the metacarpo-phalangeal joints of the index and middle fingers of the right hand are “stiff,” while those of the left are capable of a super-extension of 45° beyond the metacarpal axis; and precisely the same condition was present in his father, and has been transmitted to his son. [Illustration: FIG. 7.