An atlas of anatomy, or, Pictures of the human body in twenty-four quartro coloured plates comprising one hundred separate figures, with descriptive Letterpress / by Fenwick Miller.
- Florence Miller
- Date:
- 1879
Licence: Public Domain Mark
Credit: An atlas of anatomy, or, Pictures of the human body in twenty-four quartro coloured plates comprising one hundred separate figures, with descriptive Letterpress / by Fenwick Miller. Source: Wellcome Collection.
Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.
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![serves iiuicly ;is a sort of natural ear-trumpet, collecting sounds and aiding them to enter the ear ; and of the pass- age which leads from the exterior to the membrane of the drum of tiie ear. In the external auditory meatus (14, 15) are several small glands which secrete the ear-wax. At the bottom of the meatus a membrane (the viem- bnina lijmpiini, IG) is stretched tightly across, and encloses a cavity full of air (IS) like a drum. The tympanic cavity is not wholly closed on the opposite side from the raem- l)raiia tym]iani; a small jiassage, the Eustachian lube, runs up from the pharynx, and opens into the tympanic cavity, and through this air can enter. liunniug across the cavity of the drum (as best seen on the left side in this figure) are three small bones, united together into a chain. They are shown about the natural size in the natural situation ; but below (Fig. B) they are somewhat enlarged, and separated, in order that the curious shape of each may be seen. The first one (Fig. B, a) is attached to the middle of the membraua tympani; its shape is something like that of a hammer (malleus), after which implement it is therefore named. The next one (incus) is called the avvil. It has a depression at the top, into which the head of tlie hammer is inserted. The third little bone is exactly like a .stirrup, and is thence named the stapes. Its top fits into one of the feet of the anvil, and its lower part, answering to the foot-plate of the stirrup, is fixed into a membrane which closes up an aperture in the opposite wall of the cavity (A, 20). Thus the tympanic cavity is completely bridged across by these tiny ossicles. In the opposite wall from the membrane of the drum are two openings, each filled in with membrane, like a window with glass. One has already been mentioned as having the stirrup fastened to it: that is the oval window, OT fenestra ovalis. The other is lower down (shown just to the right of the figure 19), and is round in shape; it is called the fenestra rotunda, or round window. Past those windows, on the other side of the bone in which they are, is the internal ear, or lalnjrinth. The latter name has been given to it from the exceeding complexity of its detailed structure. It is partly made of bone and partly of membrane ; or, as it might be put, there are certain excavations made in the bone of the head, and membranous structures are found within those bony passages. Fig. C shows the bony labyrinth laid open. It is divisible into three parts : on the one side the semieircular canals (9, 10,11) ; on the other the cochlea (2, .3, 4); and a central part with which both the others communicate, the vestibule (5, 6, 7). _ The semicircular canals, three in number, open into the vestibule by only five ends, two of them joining together, and so having one common aperture. Within them, in the natural state, lie membranous semicircular canals, which open into a membranous vestibule enclosed in the bony one. These membranous structures form closed bags. They are considerably smaller than the bone in which they lie, and are separated from it by a surrounding fluid (the peii- hjmph), in which they float. The membranous canals and vestibule also contain a fluid inside them (the endohjmph), in which are found minute particles of stone. The mem- branous canals, like the bony ones (Fig. C), widen out a little near their ends where they enter the vestibule ; those expansions are called the ampullce, and inside them are found cells, which have attached to their ends little stiff hair-like projections that stand out into the cavity of the ampulla\ A part of the nerve of hearing is spread out in a network in the midst of the cells of the ampullse. The Cochlea also consists of a bony portion and a membranous portion, but these are more intricate in arrange- ment. The cochlea receives its name from its general resemblance to a snail's shell. It consists, in the first place. of a roundabout passage, excavated out of the hard bone of the head so as to turn upon itself (as a spiral staircase does) two and a half times (A, 19 ; C, 2, 3, 4). The exact middle of this e.xcavated coil is occupied by a straight pillar of bone, which stops a little short of the very top of the coil, so as to leave above it a dome called the cupola (D, 8). The pillar itself is called the modiolus. It is not perfectly solid, but is channelled by numerous small pass- ages through which the auditory nerve fibres pass (D, 7). A tliin plate of bone, the lamina spiralis ossea, twines around the modiolus, its twists corresponding to those of the sides of the cochlea. It is clear that if this bony spiral went right across from the modiolus in the centre to the side, each twist of the cochlea would be divided into two halves—one above and one below the lamina spiralis. But it does not go more than half-way across ; then the bone ends, and two delicate membranes start from it, and continue across to the sides. These membranes diverge as they go, and are affixed to the outer bone at some dis- tance (microscopicallj-, of course) from one another, so that another passage is enclosed between them. Each turn of the cochlea is thus divided into three passages—one above the lamina spiralis, one beneath it, and the third enclosed within the membranes which arise from the edge of it. (Consult carefully D, 1, 2, 3.) The space contained between the two membranes, being the centre one, is called the scala media. The passage beneath this communicates with the cavity of the drum by means of the round window (C, 1), and is therefore called the scala tympani. The passage above the scala media opens into the vestibule, and is therefore named the scala vestibuli. In Fig. E we have a diagrammatic representation of a transverse section of the cochlea, and this merits careful study. 1 is the scala tympani, and above it, 5, is the basilar membrane, by which it is separated from 2, the scala media. 6 is the other of the two membranes which take their rise from 4, the lamina spiralis. It is named the mem- brane of Ileissner, and it separates the scala vestibuli, 3, from the scala media. The lamina spiralis is here (4) seen to be composed of two thin plates of bone, between which the auditory nerve's branches run to be finally distributed on the basilar membrane, and in close connection with those remarkable structures which are figured lying upon the basilar mem- brane. These elaborate and curious structures form Corti's organ. They are, of course, excessively minute ; so minute, indeed, that their anatomy and physiology are stUl some- what uncertain. The organ of Corti is bounded above by a delicate membrane (9), between which and the basilar membrane (5) are seen splierical cells (10, 13, 17); cells which bear along their tops a number of fine hair-like processes, and which are therefore called the hair-cells (1.5); and finally the curious rod-like bodies called the fibres or rods of Corti. These latter are club-shaped bodies, set up on end so as to lean against one another and leave a triangular space beneath them (11, 12). It is believed that filaments of the nerve project into the triangular space. The latest investigations, indeed, lead to the belief that the nerve ends in the hair-cells. In any case the terminal fibres of the nerve are certainly in close relation ivith the rods of Corti. There are an immense number of Corti's rods set all .along the basilar membrane, from top to bottom of the length of the spiral coil, giving it an appearance like the key-board of a piano. Such, leaving aside a few exceedingly minute details, is the structure of the organ of hearing. A few words will explain as much of the physiology of the sense as is at present clearly known. Sound is the result of vibrations of the atmosphere striking upon the terminations of the auditorj- nerve in their](https://iiif.wellcomecollection.org/image/b21212922_0027.jp2/full/800%2C/0/default.jpg)
