516 



EMBRYOLOGY. 



Fig. 290. Cross section through the head of an embryo Pig 3 cm. 

 long, crown-rump measurement. 



The nasal cavities are seen to be in communication with the oral 

 cavity at the places designated by a * ; A', cartilage of the nasal 

 septum ; m, turbinal cartilage ; /, organ of JACOBSON ; /', the 

 place where it opens into the nasal cavity ; gf, palatal process ; 

 of, maxillary process ; zl, dental ridge. 



The horizontal palatal processes of the upper jaw increase in size, 



and finally their 

 free edges en- 

 counter in the 

 median plane the 

 still broad nasal 

 septum, which has 

 grown down yet 



f^Jj \ farther into the 



'' fe* a Di 



oral cavity. Then 

 the parts men- 

 tioned begin to 

 fuse with one an- 

 other from before 

 backward. 



Two stages of 

 this process are 

 illustrated by the 

 accompanyin g 

 figures (figs. 290, 



291), in which cross sections through the anterior end of two embryo 



Pigs are repre- 

 sented. Figure 



290 shows the 



stage at which 



the palatal 



plate (gf ) of 



the maxillary 



process (of) 



has advanced 



close to the 



lower margin 



of the nasal 



septum. Oral 



and nasal cavi- 

 ties are still 



in communica- 

 tion by means 



of the very 



narrow palatal fissure indicated by an asterisk. 



In figure 291 the fusion has taken place. In this manner the 



u 



k 



m 

 J 



Fig. 291. Cross section through the head of an embryo Pig 5 cm. 



long, crown-rump measurement. 

 k, Cartilaginous nasal septum ; m, nasal turbinal process ; /, JACOBSON'S 



organ with jk, JACOBSON'S cartilage ; zl, dental ridge ; bl, covering 



bone. 



