694 



Comparative Morphology of Chordates 



■COCHLEAR NERVB 

 -COCHLEAR DUCT 



EUSTACHIAN TUBE 



Fig. 518. The human ear: highly diagrammatic. In life the apex of the cochlea 

 lies toward the Eustachian tube. In the figure it is rotated 180 degrees. (After 

 Howell and Czermak. Courtesy, Neal and Rand: "Chordate Anatomy," Phila- 

 delphia, The Blakiston Company.) 



"hammer" is attached to the tympanic membrane and its head rests 

 upon a compactly formed solid little bone, the "anvil." The usual 

 stirrup-like form of the third bone results from the fact that, at an 

 early stage in its development, it is pierced by a small artery, a branch 



Anterior process of malleus 



anubrium of malleus 



Fig. ")14. The auditory ossicles of the human left 

 middle ear, viewed from the anteromedial aspect. (X 4.) 

 (After Henle. Courtesy, Jackson: "Morris' Human 

 Anatomy," Philadelphia, The Blakiston Company.) 



of the internal carotid. In adults of some insectivores and rodents this 

 stapedial artery persists, passing through the hole in the stapes. In 

 most mammals the artery is only temporarily present, but meanwhile 

 the stapes becomes ossified and disappearance of the artery leaves the 

 empty hole through the bone. In monotremes, some marsupials, and 

 pangolins (Manis), the stapes is solid and elongated, resembling the 



