No. 571] PATTERN DEVELOPMENT 405 



white marking seems to be a primary break, as in Fig. 25, 

 from the shoulder back of the foreleg, which delimits the 

 posterior border of the shoulder patch. In the horse the 

 shoulder patch is large, and differs from that of any 

 mammal I have yet studied, in its great extent forward 

 along the dorsal side of the neck nearly to the head. In 

 Fig. 26 a small break at the back of the neck indicates the 

 beginning of separation between the ear and the neck 

 patches dorsally, and a long tongue of white running up- 

 ward from the forearm indicates tlie anterior limit of the 

 shoulder patch. This limit is marked still nearer the 

 dorsal line in Fig. 27 by a white spot on the side of the 

 neck near its base. In Fig. 28 the shoulder patch has 

 entirely dropped out and the white space outlines very 

 nearly its extent. The ultimate center is perhaps shown 

 by the small shoulder spot in Fig. 31. 



The area covered by the ear patches extends well on to 

 the upper part of the neck, and in Fig. 29 is shown at its 

 greatest spread, or, as in Fig. 28, cut off by a narrow white 

 collar from the neck patch. The neck patch is remarkable 

 from the fact that in its areal reduction it becomes re- 

 stricted first dorsally, and the ultimate center of each side 

 is nearly ventral on the throat, so that, as generally seen, 

 the two centers form a single median patch on the front 

 or ventral part of the throat. In Fig. 26 the neck patch is 

 seen to pigment the anterior side of the forearm and is 

 partly separated from the shoulder patch by a long 

 tongue of white. It seems to extend up diagonally to 

 reach the mid-line of the neck for a short distance only, 

 as indicated in Fig. 28, where its bounds are only slightly 

 contracted. In Fig. 29 it is so far lessened as to be absent 

 from the forearm, though still in contact at the throat 

 with the ear patch where, however, a deep indentation 

 locates the dividing line between the two patches. In 

 Fig. 31 a median ventral division of the conjoined neck 

 patches is seen indicated at the upper part of the area, 

 which in this case no longer reaches the ear patches. 

 Still further reduction of both ear patches and neck 



