392 CHARLES R. STOCKARD 



Ls-bb condition is well illustrated, however, by two of the 

 F. hybrids in plates 19 and 20. 



The skeletons of the tails and the right front loos from 

 this litter of four backcross bulldog-bassethound hybrids are 

 illustrated in plate SO. The long-straight tail (fig. 1) shows 

 the perfect condition of the caudal vertebrae, all of which 

 are freely articulated in a straight line arrangement. Figure 

 •2 shows the short tail with a dorso-ventral bend and ankylosis 

 and suppression of vertebrae near its base. There are also 

 two short, deformed vertebrae near the tip, though in the 

 photographs from life this tail seems almost straight. Figure 

 :> shows another tail skeleton, much shorter than the normal, 

 with an ankylosed bend and short deformed vertebrae near 

 its tip. This bend turns the tail toward the left and is thus 

 more conspicuous from the ventral aspect than would be the 

 dorso-ventral bend in the previous case. Figure 4 is the 

 typical screw-tail, which not only has four bends, one of 

 which is vertically over another and difficult to see in the 

 photograph, but also a twisting of some of the vertebrae 

 which causes rotation of their ventral surfaces into dorsal 

 position. The angles formed by bending are permanently 

 ankylosed. 



These growth reactions bring out very emphatically the 

 fact that the deformity of the tail depends directly and 

 step-by-step upon the genetic composition of the individual 

 and is in no recognizable way related to modifications in 

 endocrine secretions. The very extreme type of bulldog-head 

 may be present in an animal with a long straight tail, and 

 vice versa, a fairly normal and long muzzled head may be 



PLATE 79 



EXE'LAXATIOX OF FIGURES 



Tail length and structure in our Litter of hybrids obtained by backcrossing the 

 !••, bassethound-English bulldog with the pure bulldog. 



l.-ind.-, 14812 (Ls-Stb). 3 and 7 1478 c? (ss-Stb). 



2and6 1479 c? (ss-Stb). 4 and 8 1482$ (ss-bb). 

 9 (LtoR) 14819, 1479c?, 1482$, 1478 c?. 



