504 



has led to considerable study of the caudal vertebrae in man ^) no 

 special account of the variation in their number need here be given. 

 The presence of haemal processes, to which attention was called by 

 Harrison, and of dorso-lateral articulating processes on the caudal 

 vertebrae is noted in the table. We shall here confine our attention 

 to the numerical variations in the thoracic, lumbar and sacral regions 

 of the embryos studied. 



Among the thirty-two embryos belonging to the Mall collection, 

 four 12,5 ^/o, show numerical variation in the precoccygeal region: 

 XVII, 18 mm; 7 c, 11 t, 6 1, 5 s, 4 Co = 33 



{12 „ 5 „ 5 „1 

 113 „ 5 „ 4 „1 

 13 „ 4 „ 5 „ 



12 |4 " ^ 

 1^ " 15 „ 5 



In each instance the variation is localized at the extremity of 

 the lumbar region and is compensated. In two instances (XLV and 

 CLXXXIV) the 25th vertebra is asymmetrical. 



Of the nine embryos described by Rosenberg, five (IIIi, 19 mm; 

 III3, 20 mm; IVia, 20 mm; IV5 and V,, 48 mm) seem to have the 

 normal number of the various vertebrae. In the following four there 

 are marked variations from the normal: 



III2, 20 mm; 7 c, 13 t, 5 1, 6 s, 4 Co. 

 IV„ 23 „ 7 „ 13 „ 4 „ 5 „ ? „ 

 IV 3, .'* „ 7 „ lo „ 4 „ 5 „ 5 „ 

 IV3A, 25 „ 7 „ 13 „ 4 „ 5 „ 5 „ 



In three of these there is an extra rib, in one there is as well a 

 distinct distal position of the sacrum. 



Of the five embryos of the His collection, three (Z.U., F.M. and 

 So.) are normal; while two (Lo, 29 mm, and SSI, 29 mm) have six 

 sacral vertebrae. 



The following table shows the extent of numerical variation found 

 in the 46 embryos tabulated above: 



1) Embryos with 24 presacral vertebrae, .... 43, 93.5 ^/^ 



a) Normal arrangement, 36, 78.3 "/<, 



b) Variation at the thoracico-lumbar margin: 



7 c, 11 t, 6 1, 5 s, 4 Co, 1, 2.2 Vo 

 7 „ 13 „ 4 „ 5 „ 4 „ + 4, 8.7 Vo' 



c) Variation in the number of sacral vertebrae, 2, 4.4 ®/o 



7 c, 12 t, 5 1, 6 s, 4 Co, (2) 



1) For the literature consult Steinbach (1899), Harrison (1901) 

 and Unger and Brugsch (1903). 



