290 



THE DEVELOPMENT OF THE CHICK 



the hind-brain and bends in above it towards the middle line (Fig. 

 168). The right and left sacci are, however, still separated by 

 a considerable space. The walls of the saccus already form a 

 large number of low folds, presumably glandular, the first begin- 



FiG. 168. — Transverse section through the head of a chick embryo of eight 



days in the region of the ear (photograph). 



C. a., Anterior semicircular canal. C. h., Horizontal semicircular canal. 

 Caps, and., Auditory capsule. Cav. Tymp., Tympanic cavity. Col., Colu- 

 mella. Duct end., Endolymphatic duct. ex. au. M., External auditory 

 meatus. Fis. Tub., Tubal fissure. Lag., Lagena. M. C, Meckel's cartilage. 

 Myel., Myelencephalon. N'ch., Notochord. p'l.. Perilymph. Sac, Saccu- 

 lus. Sac. end.. Endolymphatic sac. Tub. Eust., Eustachian tube. Tymp., 

 Tympanum. L^tr., Utriculus. X., Sac derived from the inner extremity 

 of the tympanic cavity. 



nings of which were visible on the sixth day. The form of the 

 saccus and ductus endolymphaticus at a somewhat later stage 

 is shown in the reconstruction (Fig. 173). 



