156 



THE DISSECTION OF PIG EMBRYOS FOR STUDY 



angle of the mouth back to the external ear on each side. The incisions are then 

 continued through the neck in a plane parallel to the hard palate. Before mount- 

 ing the preparation, remove the top of the head by a section cutting through the 

 eyes and nostrils parallel to the first plane of section. Transverse sections 

 through the snout may also be prepared to show the positions of tongue and 

 palatine folds before and after the fusion of the latter. 



In the human embryo of two and a half months, three palatine anlages are 



Nasal septum 



Tongue 

 Lat. palatine process 



Nasal septum 

 Lat. palatine process 



Mandible 



B 



Fig. 146. — Sections through the jaws of pig embryos to show development of the hard palate. A, 22 



mm; B, 34 mm. X 8. 



developed: a small median process developed from the fused median nasal pro- 

 cesses, and paired lateral palatine processes developed from the maxillary pro- 

 cesses, and extending from the line of fusion of the median nasal process and of 

 the maxillary process caudally along the wall of the pharynx (Fig. 148). In 

 pig embryos (Fig. 147 A and B), the median process forms a single heart-shaped 

 structure. The lateral palatine processes He at first lateral and ventral to the 

 dorsum of the tongue and their edges are directed ventrad and mesially (Fig. 

 146 A). Before these processes can fuse, the tongue is withdrawn from between 



