44 



Vertebrate Embryology 



The Nose 



The nose, like the eye and ear, begins at a 

 very early period, and is first seen as two 

 thickenings of the inner layer of the ectoblast, 



Fig. i6. — The brain of the frog. (After Marshall.) Figure 

 on left is a dorsal view ; figure on right is a ventral view. 



C, cerebellum. C//, cerebral hemisphere. CP, choroid plexus of third ven- 

 tricle. F^ fourth ventricle. I N^ tuber cinereum. M, medulla oblongata. Oy 

 olfactory lobe. (9 C, optic chiasma. O L, optic lobe. P, stalk of pineal body. 

 P By pituitary body, T^ thalamencephalon. 



/, olfactory nerve. //, optic nerve. ///, third or motor oculi nerve. /F, 

 fourth nerve. K, fifth or trigeminal nerve. I'l, sixth nerve. VJI and Vllly 

 combined root of facial and auditory nerves. IX and A", combined root of glosso- 

 pharyngeal and pneumogastric nerves. 



one on each side of the anterior end of the 

 head. An invagination of bothlayers of the ecto- 

 blast now takes place (Fig. 22, OF^, forming 

 the nasal pits whose openings to the exterior 



