HISTORY OF THE CARNIVORA 521 



for the passage of the internal carotid artery. The neck, body 

 and tail are of moderate length and the vertebrae of the loins 

 are not conspicuously large and heavy. There is no collar- 

 bone. The limb-bones have a distinct, though superficial, 

 resemblance to those of hoofed animals ; the humerus has no 

 very prominent ridges for the attachment of muscles and no 

 epicondylar foramen, and the femur no third trochanter. The 

 fore-arm bones are separate, but are so articulated together 

 and with the humerus as to give the fore foot no power of 

 rotation. The manus in all existing wild species has five digits, 

 though the pollex or first digit is very small, a mere dew-claw ; 

 the four functional digits are arranged in two symmetrical 

 pairs, very much as in the artiodactyls, a longer median pair, 

 of which the metacarpals have a nearly square cross-section, 

 and a shorter lateral pair (2d and 5th) of more trihedral 

 form. All the metacarpals are closely appressed and almost 

 parallel. The pes has four digits arranged in similar fashion. 

 The claws are blunt and non-retractile, and are of little use in 

 seizing or lacerating prey, but are useful in digging. The 

 ungual phalanges have no bony hoods reflected over the base 

 of the claw. All modern forms are digitigrade. 



Materials are lacking for the construction of any such 

 detailed phylogeny of the dogs as has been accomplished for 

 many ungulates. Many of the extinct genera are known 

 only from skulls, or even jaws, and the well-preserved skulls 

 are too few to form . distinctly defined and continuous series. 

 On the other hand, there is every reason to believe that the 

 canine genera of the successive geological stages did approx- 

 imately represent the successive steps of development within 

 the family, though it is diflScult to distinguish between the 

 phyla. 



The Pleistocene dogs, for the most part, differed little from 

 the Recent ones ; there were some very large species like the 

 Canis '\dirus (Frontispiece) of the Mississippi Valley and the 

 Pacific Coast. Two very peculiar genera have been reported. 



