Abnorynal Development of Toad Ova 23 



Peripheral Nerves — The ganglion of the trigeminal nerve is 

 highly developed. In section d a portion of it may be seen on 

 each side of the midbrain. The main branches of the nerve may 

 be followed for some distance from the ganglion. The ganglion 

 of the facial nerve is still so close to that of the auditory nerve that 

 no sharp line of division can be seen in the sections. The glosso- 

 pharyngeal and vagus ganglia are likewise still difficult to differen- 

 tiate from one another in the sections. The spinal ganglia are well 

 differentiated. The motor and sensory roots and the main trunks 

 of the spinal nerves may be distinguished without difficulty. 



Alimentary Canal — The lips and beak are highly developed. 

 Section a shows on each side of the oral opening a section of the 

 lower jaw tipped by an epithelial tooth. The operculum is 

 attached to the ventral and right sides of the body posterior to the 

 gills. Section e shows the opercular cavity near the anterior end 

 of the heart. The internal gills are of considerable size. Only 

 traces of the external gills remain. Over the region of the heart 

 the ventral wall of the pharynx gives rise to a medial projection 

 which extends in a posterior direction in the pharynx. Near the 

 tip of this the trachea arises as a solid column of cells from the 

 ventral wall of the alimentary canal near the junction of the 

 pharynx and oesophagus. More distally two tubular pulmonary 

 processes extend back one on each side from the trachea along the 

 dorsal wall of the body cavity. These do not reach so far as the 

 anlage of the pancreas. The oesophagus narrows rapidly posterior 

 to where the trachea is given off. It diverges at this period toward 

 the right side of the body (see section /, immediately in front of and 

 at the left of the chorda dorsalis). It joins the stomach in front 

 of the pancreas. In section /, on the left side of the figure (right 

 side of the body), the stomach is shown cut through in two places 

 and between these two sections of the stomach the anterior por- 

 tion of the pancreas shows on each side. The two regions of the 

 stomach here shown are joined together anterior to this section. 

 The ventral portion is joined with the oesophagus posterior to the 

 level of the section. The dorsal portion of the stomach shown in 

 this section passes posteriorly into a much coiled intestine. Part 

 of the coils of the intestine pass ventral to the heart, anterior to the 



