102 THE STRUCTURE OF THE FOWL 



The inner ear, containing the essential parts 

 of the organ of hearing, is embedded in the 

 temporal bone medial to the tympanum and 

 consists of a bony and a membranous labyrinth. 

 The former consists of a central cavity, or 

 vestibule, from which proceed three semi- 

 circular canals and a cochlea. The cochlea 

 differs from the corresponding tube of mammals 

 in being short and only slightly curved instead 

 of spirally coiled. The membranous labyrinth 

 is divisible into two parts. The superior part 

 consists of a utricle and two sinuses (posterior 

 and superior) and three semicircular ducts, 

 each with an ampulla. The semicircular ducts 

 are superior, posterior, and lateral, and are 

 arranged along different planes of the head. 

 The superior duct is in a vertical and longi- 

 tudinal plane ; the posterior duct lies in a 

 transverse and vertical plane ; the lateral 

 duct is practically horizontal. The inferior 

 part of the membranous labyrinth consists of 

 a cochlear duct and a saccule with which is 

 connected an endolymphatic duct ending as a 

 small sac in the dura mater within the cranium. 

 The saccule may be regarded as an appendage 

 to the utricle. The cochlear duct contains 

 the essential organ by which sound waves are 



