ORGANS OF SENSE. 61 



found in all mammalia, except the cetacea, the glandula Harden 

 exists in the carnivora, ruminantia, pachydermata, and some roden- 

 tia. Instead of puncta lachrymalia, the hare and rabbit have a slit 

 opening into the nasal duct ; the eye is moved by four recti and 

 two oblique muscles, and in many of the genus felis the superior 

 oblique is perforated by the rectus superior : the inferior oblique 

 has the same relation to the inferior rectus in the tiger, though not 

 in the lion. All the muscles of the eye are said to be wanting in 

 those animals in which the organ is in a rudimentary state. 



Hearing. — When we consider the many services arising from 

 this sense, such as indicating the approach of danger, conducting 

 predaceous animals to their prey, the bringing together the two sexes, 

 (fee, we should expect to find, as we really do, an organ of hearing 

 in almost every division of the animal kingdom. In the radiated 

 division of animals no distinct acoustic organs have been detected ; 

 it is probable, however, that the undulations produced by the per- 

 cussion of outward bodies in the media in which these low creatures 

 reside, produce some impression, though feeble it may be, upon the 

 general surface of their bodies. It is not till we ascend in the scale 

 as high as the active air breathing insects of the articulata that we 

 meet with special organs appropriated to this sense ; and here they 

 consist of auditory nerve, vestibule, and two rudimentary semicir- 

 cular canals. In many of the inferior torpid mollusca there do not 

 seem to be any particular organs devoted to the perception of sound, 

 but in the higher cephalopods which approach the nearest to fish 

 in their general characters, the organs of hearing present a similar 

 degree of complexity. 



Fishes, like the cephalopodous mollusca, receive their acoustic 

 impression by undulations through the dense medium surrounding 

 them, and in the lowest cartilaginous species, as the lamprey, the 

 organ consists of a simple vestibule, and three membranous semi- 

 circular canals, separated from the cavity of the skull merely by 

 dura mater. In the bony fishes the vestibule and semicircular 

 canals are highly developed, fenestra ovalis appears, and by and by 

 a rudimentary cochlea and tympanum without air are seen ; in the 

 cavity of the vestibule two or three small bodies are found, soft and 

 pulpy in the cartilaginous fishes, but of a stony hardness in the 

 osseous kind, and composed of carbonate of lime. 



In the aquatic amphibia and in the tadpole state of the reptiliform 

 species, the organ of hearing possesses a near affinity to that of 

 fishes ; it consists of the vestibular cavity containing its cretaceous 

 bodies, the membranous semicircular canals, and fenestra ovalis 

 closed by stapes, all contained in a cavity of the temporal bone, and 

 covered externally by the common integument. But in the adult 

 state of the frog and salamander the apparatus is more complicated, 

 the semicircular canals are lodged in the temporal bone ; the tym- 

 panum is closed by membrana tympani, contains three ossicula 

 united, and communicates with the fauces by a Eustachian tube. 



The reptiles present a higher development of acoustic organs ; in 



