46 NATURAL THEOLOGY. 



Spoken ; in large quadrupeds, turning to the sound, 

 and possessing a configuration, as v.ell as motion, 

 evidently fitted for the office : of a tube which leads 

 into the head, lying at the root of this outward ear, 

 the folds and sinuses thereof tending and conduct- 

 ing the air tow^ards it: of a thin membrane, like the 

 pelt of a drum, stretched across this passage upon 

 a bony rim : of a chain of movable and infinitely 

 curious bones, forming a communication, and the 

 only communication that can be observed, between 

 the membrane last mentioned and the interior chan- 

 nels and recesses of the skull : of cavities, similar 

 in shape and form to wind instruments of music, 

 being spiral or portions of circles : of the eusta- 

 chian tube, like the hole in a drum, to let the air 

 pass freely into and out of the barrel of the ear, 

 as the covering membrane vibrates, or as the tem- 

 perature may be altered : the whole labyrinth hewn 

 out of a rock ; that is, wrought into the substance 

 of the hardest bone of the body. This assemblage 



bone. The second bone is the incus, or anvil, to the grooved sur- 

 face of which the malleus is attached. A long process extends 

 from this bone, which has upon it the os orhiculare; and to this 

 third bone there is attached a fourth, the stapes, which is in shape 

 like a stirrup iron. The base of this bone is of an oval shape, and 

 rests upon a membrane which closes the hole leading into the 

 labj-rinth. This hole is called foramen ovale. The plan of the 

 cochlea shows that one of its spiral passages, beginning in the ves- 

 tibule, winds rotmd the pillar till it meets in a point with another 

 tube. If the eye follow this second spiral tube, it will be found to 

 lead, not into the vestibule, but into the irregular cavity of the 

 tympanum. 



