AS TO THE HEREBiTt OF ACQUIRED CONDITIONS. 467 



by the last-named writer, when lie says " they [i. e. the imperfect 

 digits] represent the amount of vitality left in the embryonic cells 

 from which the extremities of the limb should have developed." 

 We explain the presence of extremities on sacral tumours repre- 

 senting an imperfect parasitic twin, such as those of Anna Maria 

 Przesomj'l and the other given by Braune *, by supposing that the 

 cells forming that portion of the limb have come to development, 

 whilst others have failed to do so ; and there seems no reason why 

 a similar explanation should not be given in the cases under 

 consideration. Passing from these special groups, it may next 

 be mentioned that Erlich f has grouped congenital defects of 

 extremities into the following divisions : — (1) deficiency of forma- 

 tive material (Anlagekeim) ; (2) deficiency of division or segmen- 

 tation (Grliederung) where a ray (Tibia, Eadius, with tarsals or 

 carpals, &c.) is absent ; (3) deficiency of growth from injury to 

 cartilage or bone, Ecetal Rachitis ; (4) spontaneous amputation, 

 or strangulation. 



"We have now to consider the bearing of the facts just detailed 

 upon the section of the subject now under discussion. First of 

 all we may dismiss, I think, the subject of peromelia, since I am 

 not aware that it has ever been described as hereditary in man. 

 Sfc.-Hilaire J has given an account of one case in which it was 

 hereditary in dogs, and I know of no other of any kind. Pero- 

 dactyly is, however, not uncommonly hereditary. In a case 

 given by Potherby §, the hands and feet were both afi'ected, only 

 great and little toes being present in the latter ; the malforma- 

 tion ran througli five generations. Other cases have been given by 

 Holmgrenll, five generations ; Krabbe^f, three; and Lucas, four**. 



In considering the nature of this defect it should be borne in 

 mind that there are several preliminary conditions, so to speak, 

 leading up to it and often merging into or blending with it, none 

 of which could be caused by amniotic agencies. Thus Annandale 

 gives the following degrees of union of digits, a condition 



* ' Die Doppelbild. u. angeb. G-eschw. d. Kreuzbeingegend,' Leipzig, 1862, 

 Taf. iii. figs. 1, 2, 3, & 7. 



t " Untersuch. iib. d. Cong.-Def. u. Hemmungsbild d. Extrem.," Virch. Arch. 

 Bd. 100. S. 107. I 02). cii. vol. ii. p. 670. 



§ Brit. Med. Journ. May 22, 1886. 



II Upsala lakareforen. forhandl. xvii. 7 og 8, S. 513 ; Abstr Schmidt's Jahrb. 

 Bd. 196. S. 121. 



^ Nord. Med. Ark. xii. 20. S. 1 ; Abstr. Schmidt's Jahrb. Bd. 19(3. S. 121. 



** Traite de rH6redit6 Naturelle (Paris, 1847), p. 198. 



83* 



