38 AVERS. [Vol. VI. 



COCHLEA (lAGENA). 



In this account of avian cochlea no mention is made of the 

 scala vestibuli or tympani, but only of the endolymphatic tube, 

 or cochlea proper, — scala media. The cochlea of the Mocking- 

 bird is an elongated pocket hanging down from the floor of the 

 sacculus. In length it equals more than half of the vertical 

 height of the whole ear and approximates one-third its length. 

 Its diameter in the adult is greater than that of the sacculus. 

 Its course, referred to the planes of the body, is downwards, 

 inwards, and backwards. Its general shape and the main ana- 

 tomical features do not differ materially from those of the 

 pigeon, as described by Hasse and Retzius. 



The lagena is relatively larger and more sharply marked off 

 from the basilar portion than it is in the pigeon, and the latter 

 part is more distinctly triangular in shape, with its base joined 

 to the sacculus by means of the narrow canalis sacculo-cochlearis. 



The cochlear canal is doubly curved, i.e. it has the form of 

 the basal part of the cochlear canal of the Mammal ear, but 

 projects from the saccular region more nearly perpendicular to 

 the vertical axis of the whole organ than does the cochlea in the 

 latter group. 



The first curve is a bend transverse to its long axis and affects 

 the upper portion of the tube most ; the second curve is more 

 equally distributed throughout the length of the tube. The 

 upper two-thirds of the canal is occupied by the basilar sense 

 organ, while the lower third is taken up by the constriction 

 which marks off the lagenar pocket. 



The lagenar pocket is nearly filled with the lagenar sense 

 organ, the floor of the pocket, with the exception of a border 

 all around, being covered by the sensory epithelium. 



Already in the bird the pseudo-cartilaginous oval frame which 

 supports the cochlear organs has made good progress toward 

 forming a protective case for the whole cochlear apparatus. 

 By the fusion of the lateral bars of the frame in the lower half 

 of their- course the scala tympani is inclosed with the cochlear 

 duct. The fibres of the cochlear nerve enter the cartilage at 

 once after leaving its ganglion in the form of a continuous sheet 

 of threads, and passes through the edge of the basilar membrane 

 to be distributed to the sensory cells on its vestibular surface. 



