ANATOMY. 



The cavity of the tympanum contains a 

 cliain of small bones called ossicula audi- 

 tus, connected by one end to the membra- 

 na tympani, and by the other to the fe- 

 nestra ovalis. Of these the first, which is 

 compared to a hammer, is called the mal- 

 leus ; the second is named the incus, the 

 third the orbiculare, and the fourth the 

 stapes. 



The malleus possesses a manubrium or 

 handle, a long and short process, and a 

 head which forms an articular surface. 



The incus resembles a grinding- tooth, 

 with its two fangs diverging. We remark 

 in it a body, the surface of which is hol- 

 lowed out to receive the head of the mal- 

 leus ; a long and a short leg. 



The orbiculare is of the size of a small 

 grain of sand. It is attached to the ex- 

 tremity of the long crus of the incus and 

 the stapes. 



The stapes has an exact resemblance 

 to the iron part of a stirrup : it has a head, 

 two crura, and a basis. 



The handle of the malleus is firmly con- 

 nected to the membrana tympani ; and 

 hence arises the external concavity and 

 internal convexity of the membrane. The 

 head of that bone is joined to the body of 

 the incus, whose long leg is articulated to 

 the head of the stapes. The basis of the 

 stapes fills up the fenestra ovalis. The 

 ends of the bones forming these articula- 

 tions are covered with cartilage, and fur- 

 nished with capsules like other joints. 



The bones of the tympanum have some 

 smallmusclesconnected to them by which 

 they are moved outwards, or towards the 

 membrana tympani, and inwards, or to- 

 wards the fenestra ovalis. The first of 

 these motions relaxes, the latter stretches 

 the membrane. The names of these mus- 

 cles are, tensor tympani, laxator tympani, 

 and stapedeus. 



The nerve called chorda tympani passes 

 across the tympanum, between the handle 

 of the malleus and the long leg of the 

 incus. 



The use of the ossicula auditus seems 

 to be that of transmitting the vibrations of 

 the air from the membrana tympani to the 

 labyrinth. The final use of the muscles 

 which moves these bones is unknown. 



The labyrinth of the ear consists of 

 three parts: 1. A spiral bony canal, 

 twisted like a snail-shell and thence call- 

 ed the cochlea. 2. Three semicircular 

 bony canals : and 3. A sm.ill cavity, call- 

 ed the vestibulum, into which the cochlea 

 and the semicircular canals open. These 

 parts are formed of the hardest bone in 

 the body, almost equal in solidity to ivory, 



and the petrous portion of the temporal 

 bone, which incloses them, is of a similar 

 structure. In the foetus the labyrinth is 

 surrounded by a softer and looser kind of 

 bone, so that it can be most easily dissect- 

 ed at that age. 



The vestibulum is about equal in size 

 to a large pea, and the fenestra ovalis 

 opens into the middle of the cavity. It 

 has also five openings from tlie semicir- 

 cular canals ; the superior and exterior 

 joining by one of their extremities, and 

 opening by a common hole. 



The cochlea has two turns and a half. 

 Its canal turns round a bony centre, called 

 the modiolus, to which is attached a thin 

 plate of bone, projecting into the cavity 

 of the cochlea, and named lamina spiralis. 

 This projecting plate divides the canal of 

 the cochlea into two parts : one opening 

 into the vestibulum, the other at the fe- 

 nestra rotunda. The latter is called the 

 scala tympani, the former scala vestibuli. 



The vestibulum, cochlea, and semicir- 

 cular canals are. lined by a delicate vascu- 

 lar membrane, on which the portio mollis 

 of the seventh pair of nerves are distribut- 

 ed. This membrane contains a clear 

 water. 



The filaments of the auditory nerve 

 pass from the meatus auditorius internus 

 through a number of very small apertures 

 which lead to the labyrinth, and they ter- 

 minate on the vascular membrane of the 

 labyrinth, so that the nervous pulp is ex- 

 posed almost bare to the contained fluid. 

 The distribution of the nerve on the coch- 

 lea is particularly beautiful. The aque- 

 ducts of the ear are two very fine tubes, 

 passing from the vestibulum and cochlea 

 to open on the surface of the dura mater. 



ORGAN OF SMELLIKG. 



The nose is a cavity of very irregular 

 figure, formed chiefly by the bones of the 

 face, and communicating with the various 

 sinuses, or bony cells formed in the head. 



It is separated by the brain above by 

 the cribriform lamella of the ethmoid 

 bone. This separation is a perfect one, 

 and the two cavities of the cranium and 

 nose are wholly distinct from each other, 

 although they are supposed, by the unin- 

 formed in anatomy, to communicate to- 

 gether. 



The bottom of the cavity is formed by 

 the upper surface of the pallet. 



The general cavity is divided into two 

 equal halves, called nostrils, by the sep- 

 tum narium, a thin and flat bony parti- 

 tion, descending from the cribriform la- 



