OUR FACE FROM FISH TO MAN 



In our survey of the neural part of the human cranium 

 we have seen that its outstanding features are the result 

 of a great cerebral development. When, however, we turn 

 to the facial and pharyngeal parts of the skull and head, 

 we find that the factors which have determined their shape 

 are related to the functions of smell, respiration and of 

 mastication. It is unnecessary to again insist on the fact 

 that the human embryo, in the latter part of the first 

 month, shows a resemblance to a generalized type of fish; 

 it possesses the basis of a branchial arch system. As in 

 the fish, the olfactory organ is represented by a pair of 

 pits or depressions, which at first have no communication 

 with the mouth. In some forms of fish — certain rays and 

 sharks — a channel is formed between each olfactory pit 

 and the mouth. The functional meaning of such a channel 

 is evident; the water imbibed is sampled by the nose 

 before entering the mouth. When pulmonary breathing 

 was introduced, as in Dipnoean fishes, the open naso- 

 buccal channel became enclosed by the union of its bound- 

 ing folds. In amphibians, reptiles and birds the naso- 

 buccal channel becomes dilated to form a true respiratory 

 nasal passage, and the parts bounding the passage unite 

 on the roof of the mouth to form the primitive palate. 

 In Fig. 152 the parts entering into the formation of the 

 primitive palate are shown. They are three in number: 

 (1) a premaxillary and vomerine part developed between 

 the nasal passages; (2) a right and left maxillary part, 

 laid down on the lateral or outer aspect of each passage. 

 In mammals a fourth element is added to the primitive 

 or reptilian palate, and in this way the mammalian mouth 

 is separated from the nasal respiratory passage, and can 

 serve the purposes of mastication and suction. Thus in 

 the evolution of the face there have been three distinct 

 stages: (1) a piscine, in which the nose and mouth were 

 formed independently; (2) an amphibian stage, where the 

 nasal respiratory passage opened on the roof of the mouth; 

 (3) a mammalian stage, in which it opened in the naso- 



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