

ANATOMY. 



The cavity of the tympanum contains a 

 chain of small bones called ossicula audi- 

 tus, connected by one end to the membra- 

 na tympani, and by Uie 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 amanubrium 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 ofthe 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 T,he 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 ofthe tympanum have some 

 small muscles connected to them by whirh 

 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 ofthese 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 small cavity, call- 

 ed the vestibulum, into which the cochlea 

 and the semicircular canals open. These 

 parts are formed ofthe hardest bone in 

 the body, almost equal in solidity to ivory, 



and the petrous portion ofthe temporal 

 bone, which incloses them, is of a similar 

 structure. In the fcrtus 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 ofthe cavity. It 

 has also five openings from the 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 

 ofthe 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- 

 larmembrane, on which the portio mollis 

 of the seventh pair of nerves is distribu- 

 ted. This membrane contains a clear 

 water. 



The filaments of the auditory nerve 

 pass from the meatus auclitorius mternus 

 through a number of very small apertures 

 which lead to the labyrinth, and they ter- 

 minate on the vascular membrane ofthe 

 labyrinth, so that the nervous pulp is ex- 

 posed almost bare to the contained fluid. 

 The distribution ofthe 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 8MELLLIXG. 



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 di stinct from each other, 

 although the_y 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- 



