90 PROCEEDINGS OF THE ACADEMY OF [1888. 



cauce as the sacral spot. In Dldelphys a dark pigment ring eneircle& 

 the base of the tail. In roan horses a ■white ring is occasionally 

 found which also encircles the base of the tail. 



In Thijlaeinus, Felis matnd,^Htjcna striata, Mi/nneeohlns, and in some- 

 of the viverrine genera, the line is interrupted and a number of sad- 

 dle marks are seen which are best marked posteriorly. In the dog 

 when the black and tan colors are bred out, as in the English setter,, 

 the bull terrier and the fox terrier, the dorsal line is retained only at 

 the sacrum and at the root of the tail. It often forms an irregular 

 mark which may extend upon the tiaidvs. In the " Chester reds," 

 a variety of hog bred in Eastern Pennsylvania, black is persist- 

 ently bred out, yet a small black spot is commonly found at the sac- 

 rum. In Phoca fasciata a broad white band crosses the trunk at the 

 sacral region. 



In Cercopithecus diana, the greater pai't of the dorsal region and 

 all the sacral region are of a red color which extends downward upon 

 the outer surface of the flank. 



This disposition is seen in a number of the quadrumana. It ap- 

 pears to be repeated in many dogs (as already mentioned) in which 

 a flank mark is continuous with the sacral spot. The mark may be 

 homologous with the sacral saddle mark of Thylacinus and Felis tigris* 

 In a colony of piebald rats observed at the Zoological Garden, 

 Philadelphia, the sacral region was black while the prevalent hue 

 Avas white. 



I will now attempt to explain the persistence of color marks at the 

 region of the sacrum and the root of the tail, though the varieties of 

 the colors themselves are not at present susceptible of demonstration. 

 In the range of human observation, L. Tait' records the frequent 

 possesssion — nearly 45 per cent — of a pit, or " sacral dimple," over 

 the sacral region in women. 



A. Ecker^ describes the frequent appearance of pits or depressions 

 in the region of the coccyx, in the foetus and in new-born infants. 

 The spot is associated with various pilose conditions. Max Bartels* 

 describes a tail-like formation in man from the lower part of the 

 same region. Virchow^ fluds the pilose spots co-ordinated with 



1 A. Milne Edwards, Recherches sur les Mammiferes, Paris, 1868 to 1874, 

 PI. 31. 



2 Nature, 1878 XVIII, 481. 



3 Archiv. f. Amhropologie, 1880, XII, 129. 

 * Ibid, 1881, XIII, 1. 



5 Zeitsclir f. Ethnologic 1875, VII 280. 



