The origin of the affection is very obscure. It is not hereditary, although inheritance plays a notable part in many other congenital deformities, and it cannot be attributed to any known influences arising during intra-uterine life, but, as might be expected, the mother is often able to conjure up some reminiscence of the period of gestation which to her mind affords a perfectly satisfactory clue to the mystery. Von Klein relates that in his case of makrodactyly the mother while pregnant was bitten in the hand by a goose. A history of a fright was given in Adams’s case, and in an instance reported by the author[31] a giant growth of the lower extremity was attributed to the mother having been trodden upon by a cow. Such mental impressions are probably mere coincidences, and are often greatly exaggerated in narration, but until the possibility of their connection with fœtal lesions is disproved it is advisable to place them on record. _Parts affected._—The abnormality is usually limited to one side of the body. Comparatively few bilateral cases have been observed, and in most of these the makroplasia was limited to the digits.[32] The nævi with which the hypertrophy is often associated are nearly always confined to the affected side, but in two cases of Chassaignac and Friedberg they were found also upon the non-hypertrophied side, and in a second case of Chassaignac’s were present only upon the unenlarged parts of the body. The upper extremity is attacked nearly twice as often as the lower, and the right side much more frequently than the left. In bilateral cases the affection is seldom symmetrical; thus, on one of Friedberg’s cases the predominant enlargement of the right lower extremity was associated with a small degree of hypertrophy of the left upper limb. The extent of the parts involved ranges from a single digit to an entire half of the body. When a whole limb is implicated the growth is always proportionately greater at the distal extremity, but colossal development of the hand or foot seldom includes the whole of the digits. The localisation of the affection does not appear to be related to any special vascular or nervous territories; thus, in makrodactyly, the regions of distribution of the digital branches of both median and ulnar nerves may be encroached upon, while parts supplied by either or both of these may escape intact. [Illustration: FIG. 18. Congenital hypertrophy of lower extremity, with lymphangeiomata (from a case of the author’s).] Commonly, however, both in the hand and foot, the hypertrophy selects two or three neighbouring digits, for example, the second and third; and co-existent lipomata are almost invariably limited to that portion of the palm or sole which corresponds to the enlarged fingers or toes. In the hand the digit most commonly affected is the third, the fifth is that most exempt.