148 Dynamic Theory. 



scrotal sacs. The males of several genera of Reptiles have a forked or 

 double organ of generation corresponding with the double ovary and 

 two oviducts of the female. In some cases, these two male organs are 

 so far separated from each other that one appears on each side of the 

 cloaca contained in a sac. Some reptiles of the lizzard kind possess 

 double reproductive organs. The uteri of seals are partly consolidated, 

 but still divided by a partition or septum. 



In many animals the tongue is double. This is the case with snakes 

 in general, and some lizzards. The tongue of the seal is also split at its 

 extremity. The upper lip of the rabbit is double, being cleft in the 

 middle, and so is that of the camel. The human deformity called 

 " hare-lip " is such a cleft in the middle of the upper lip, and is often 

 accompanied by "wolf's-jaw," which is a corresponding cleft or fissure 

 in upper jaw-bone and of the palate. This deformity is caused in em- 

 bryonic development by the failure of the tube of the body to close at 

 this particular part of the median line of closure along the belly side of 

 the body, and is, in a certain sense, a reversion. 



Mention has heretofore been made of the intermaxillary bone, which 

 occupies the front center of the upper jaw in apes and in the human em- 

 bryo. In most of the vertebrates, except the monkey and ape tribes, 

 there are two bones instead of one. They are called the premaxillaries, 

 and are usually joined to each other in front by a median suture, and 

 are joined at the sides by sutures to the maxillaries. This arrangement 

 is the rule throughout the vertebrate tribes fishes, amphibians, birds, 

 and mammals. There are some exceptions, however, among the rep- 

 tiles, the two bones being soldered together in some of the snakes and 

 turtles. In some of the bats they are reduced to rudiments in size. 

 But their transition development is most remarkable in the monkey and 

 ape tribes. These animals are born with the two bones. But at some 

 period of their lives the suture between the bones disappears and they 

 become one. In the Cebus ( Platyrhine Monkey of high organization ) 

 this happens in early life. Among the Baboons and Mandrils ( Cyno- 

 morpha ) the median suture does not disappear till late, occasionally 

 not at all. In the Chimpanzee it disappears when the milk teeth fall 

 out, but in the other man-like apes, not till after the second dentition is 

 accomplished. ( Huxley, Vertebrate Anatomy. ) 



Thus, most of the higher monkeys and all the man-like apes, possess, 

 in adult life, the single intermaxillary bone. As before mentioned, it 

 is developed in the human embryo, but about the time of birth, or soon 

 after, it is absorbed, and the two sutures, which connect it on each side 

 with the maxillaries, are gradually brought together till they become 

 one the bone between them quite disappearing. The double gills of 

 worms and fishes seem to be the result of direct correlation of respira- 



