偶蹄目骨骼特征 1.对称型脚趾(paraxonic limb structure): in which the symmetry of the foot passes between the two middle digits (III and IV). • 2. 大拇趾退失, 脚趾数多为偶数: The first digit (the "thumb" or pollex in the hand and the hallux on the hind limb) is absent in all modern artiodactyls, with the result that all species possess an even number of toes on each foot (with the exception of the Tayassu and Pecari of Tayassuids, in which the hind foot only has three digits). Two main types of foot structure are recognized: a "cloven hoof" with two