THE EAR. 



395 



The condition on the fifteenth day is shown in Fig. 159, the 

 section, on the left side, being taken at a level slightly anterior 

 to that of the right side. The recessus vestibuli, rat, is still 

 large, and is dilated at its upper end in a club-shaped manner. 

 The three semicircular canals are well established : they are 

 formed, as in the chick and frog, from flattened saccular out- 



CH TP 



EiG. 158. — A transverse section across the head of a Rabbit Embrj^o at the 

 end of the eleventh day, the section passing- through the medulla oblongata, 

 the ears, and the pharynx. The plane of section of the right half of the 

 figure is slightly anterior to that of the left half. (Compare Fig. 147.) 

 x30. 



CH, notochord. EB, membrane closing hyomandibular cleft. ED, common stem 

 of the two vertical semicircular canals. EEL rudiment of the external or horizontal 

 semicircular canal. EL, cochlear canal. ER, recessus vestibuli. EV, auditory 

 vesicle. HM. hyomandibular pouch. TP, pharynx. VP, fourth ventricle. VJ, 

 jugular vein. VIII, auditory nerve. 



growths of the auditory vesicle, the two walls of each outgrowth 

 coming in contact and fusing, so as to form a curved tube open- 

 ing into the vestibule at both ends. The section (Fig. 159) 

 passes through the stem common to the two vertical semicircular 

 canals, ED, and also through the horizontal canal, eh. Each 

 semicircular canal has already acquired an ampulla at one end. 



