232 CHARLES R. STOCKAED AND A. L. JOHNSON 



designed for the functions of the normal dog which were 

 so perfectly seen in the dachshund. The edges of the upper 

 and lower incisor teeth are seen in the photographs to be 

 in end to end relation. This disturbs a proper occlusion of 

 the canines which interfere with and grind against one 

 another in various ways. The premolar carrying interval 

 is very short in some Boston terrier skulls and entirely lost 

 in others. As shown in plate 38 (fig. 4), the upper fourth 

 premolar may be set transversely across the jaw, that is, 

 at right angles to the normal position for this tooth. The 

 upper molar teeth, instead of being arranged in an almost 

 straight line as in the dachshund, follow an angular course, 

 the apex of which projects out laterally. Malocclusion of 

 the molars is present to various degrees. 



The poor dental accommodation of these short, deformed 

 jaws is associated with numerous defects of the teeth them- 

 selves. Improper occlusion tends to loosen the teeth and 

 wear them down in abnormal ways. As clearly shown in 

 plate 38, resorption of alveolar bone may occur as a result 

 of improper pressure. The teeth may be defective in structure 

 with hypoplasia of the enamel; this may also be seen in the 

 photographs of the Boston terrier skulls. Figure 2 in plate 

 37 shows that the lower jaw of the Boston terrier is not 

 only short, but curved as well, with the anterior end directed 

 upward. This is in direct contrast to the long, straight lower 

 jaw of the dachshund (fig. 1). 



The differences between the skulls from these two pure 

 dog breeds are so readily distinguishable and are so numerous 

 that before attempting to compare their detailed indices and 

 measurements with those of their hybrids it would be best 

 to proceed with a general consideration of the gross appear- 

 ance of these hybrids during life. 



Photographs from life of the Boston terrier and the dachs- 

 hund and five of their F! hybrids are shown in plate 29 (p. 

 127). The hybrid skull and lower jaw are illustrated in plates 

 36 and 37 (figs. 3). The sagittal outline of the F x skull is 

 drawn in solid line in figures 2 and 3 of text-figure 56; in 



