146 



THE DISSECTION OF PIG EMBRYOS 



parts to fuse may produce hare lip. The line of fusion of the median nasal processes is evi- 

 dent in the adult as the philtrum. The lips of the newborn child are peculiar in that their 

 proximal surfaces are covered with numerous villi, finger-like processes which may be a 

 milliirieter or more in length. 



Fig. ISO. — Development of the face of the human embryo (His). A, Embryo of 8 mm. (X 7.5); 

 the median frontal process differentiating into median nasal processes or processus globulares, toward 

 which the maxillary processes of the first visceral arch are extending. B, Embryo of 13.7 mm. (X 5); 

 the globular, lateral nasal and maxillary processes are in apposition; the primitive naris is now better 

 defined. C, Embryo of 17 mm. (X 5); immediate boundaries of mouth are more definite and the nasal 

 orifices are partly formed, external ear appearing. D, Embryo of nearly eight weeks (X 5). 



The external ear is developed around the first branchial cleft by the appearance of small 

 tubercles which form the auricle. The cleft itself becomes the external auditory meatus and 

 the concha of the ear. (For the development of the external ear see Chapter XIII.) 



DEVELOPMENT OF THE PALATE 



This may be studied advantageously in pig embryos of two stages: (a) 20 to 25 mm. 

 long; (b) 28 to 35 mm. long. Dissections may be made by carrying a shallow incision from 

 the anlage of the mouth back to the external ear on each side (Fig. 152). The incisions are 

 then continued through the neck in a plane parallel to the hard palate. Before mounting the 

 preparation, remove the top of the head by a section cutting through the eyes and nostrils 



