ORGAN OF HEARING. 



529 



phalanx.* The remaining tendons of the index 

 and little finders are implanted into the pha- 

 langes of those fingers with those of the 

 common extensor : those nf the thumb are 

 inserted separately. Having no sheaths, these 

 tendons are firmly attached by means of a 

 membranous expansion to the bones to prevent 

 them slipping aside, nor have they here any 

 synovial membranes, and are therefore in con- 

 tact with those of the joints; but as they pass 

 through the sheaths in the posterior annular 

 ligament, they are all provided with synovial 

 sacs. The largest is that of the extensor com- 

 munis and indicator; they are less complex 

 than those of the palmar region, and their 

 inflammation less formidable and not so pain- 

 ful. The occurrence of ganglia is here very 

 frequent. They sometimes attain a large size 

 and produce considerable inconvenience. The 

 puncture of them is not so dangerous here as 

 in the palmar region. 



6. Arteries. The course of the radial over 

 the back of the hand has been already noticed ; 

 its metacarpal and carpal branches run across 

 the wrist beneath the extensor tendons, unite 

 with the posterior carpal branch of the ulnar, 

 forming a kind of dorsal arch, from which pro- 

 ceed the interosseous and perforating branches, 

 to communicate with the deep arch ; also the 

 dorso-digital branches, one to either side of the 

 fingers. 



The bones and ligaments forming the firm, 

 light, and compact skeleton of the hand have 

 been elsewhere described. See article HAND, 



BONES AND JOINTS. 



In the amputation of the metacarpal bone of 

 the thumb, which is easily performed at its 

 articulation with the trapezium, the edge of the 

 knife should be kept close to the ulnar edge of 

 the bone, in order, if possible, to avoid wound- 

 ing the radial artery as it traverses the inter- 

 osseous space. The metacarpal bone of the 

 little finger may also easily be removed by an 

 operation similar to that practised for the 

 thumb; the articulating surfaces are nearly 

 plane and inclined obliquely upwards and 

 inwards. Disarticulations may also be per- 

 formed of the other metacarpo-carpal joints; 

 but the operations are very difficult and em- 

 barrassing, owing to the irregularity of the 

 articular surfaces and their close connexions 

 with each other, and in removing them singly 

 a much neater and easier plan is, if their 

 upper extremities are sufficiently sound, to saw 

 through them in an oblique direction. 



In amputating at the phalangeo-metacarpal 

 articulations the flap is, if possible, made on 

 the palmar surface. At the first joint of the 

 fingers two flaps are preserved by making two 

 semilunar incisions, which extend from the 

 head of the metacarpal bones to the termination 

 of the commissure of the fingers, meeting be- 

 hind and before at the joint, which is an inch 

 above. They may all be amputated together 

 when a single flap is made on the palmar surface 

 terminating at the line in the skin that bounds 



* It is not uncommon for these tendons to send a 

 lip to th superior extremity of the first phalanx. 

 VOL. II. 



the commissure. In amputating at the other 

 joints of the fingers it is necessary to recollect 

 tilt- marks, before alluded to when speaking of 

 the skin, and to divide the lateral ligaments 

 before entering the joints. 



(F. T. M'Dougall.) 



HEARING, ORGAN OF. The ear (in the 

 wide acceptation of the term). Organon auditus 

 s. uurts. Fr. L'organe de fouie ou I'oreille. 

 Germ. Das Geh'ororgan oder das Ofir. As 

 the apparatus of vision naturally admits of 

 being divided into two parts, viz. the eye-ball 

 and its appendages, so we can distinguish in 

 the apparatus of hearing a fundamental organ, 

 and parts accessory to the perfect performance 

 of its function. The fundamental organ of 

 hearing is what is commonly called the internal 

 ear, or from the complexity of its structure, the 

 labyrinth. The accessory organs consist of the 

 middle ear or tympanum and external ear.* 



If we extend our observations to the animal 

 series, and trace the apparatus of hearing along 

 the descending scale, we shall find that the 

 accessory parts gradually disappear, and that 

 the sense of hearing comes at last to have for 

 its organ merely a representative of the laby- 

 rinth in the higher animals. This part even, 

 having laid aside much of its complicated 

 structure, presents itself under the form simply 

 of a membraneous pouch containing a fluid, 

 with a calcareous concretion suspended in it, 

 on which the auditory nervous filaments are 

 expanded. 



The labyrinth being in the apparatus of hear- 

 ing exactly what the eye-ball is in that of vision, 

 may be distinguished by the name of ear-bulb. 

 The ear-bulb, like the eye-ball, consists of a hard 

 external case, in the interior of which are con- 

 tained membraneous and nervous parts and 

 humours. The accessory parts of the apparatus 

 of hearing have also their prototypes in the 

 accessory organs of the apparatus of vision. 



The different parts of the apparatus of hear- 

 ing are situated in the interior and on the sur- 

 face of the temporal boue. See the description 

 of the temporal bone in the article CRANIUM. 



I. THE EAR-BULB, or fundamental organ of 

 hearing. ( Bulbe audit if, Breschet.) 



In man and the higher animals, the hard ex- 

 ternal case of the ear-bulb is of bone, and is 

 called the osseous labyrinth. The soft textures 

 contained in its interior bear the name of mem- 

 braneous labyrinth. The interior of the osseous 

 labyrinth, which we may with Breschetf call 

 the labyrinthk cavity, is not completely filled 

 by the membraneous labyrinth ; the remaining 

 space is occupied by a limpid watery fluid. 



1 . The osseous labyrinth (tabyrinthus osseus , 

 Fr. Labyrinlhe osseujc ; Germ. Das knocherne 

 Labyrinth.') The osseous labyrinth presents 

 three compartments, distinguished by the names 



* Haighton, in Memoirs of the Medical Society 

 of London, vol. iii. p. 7. London, 1792. 



t Recherche* anatomiques et physiologiques sat 

 1'organe do 1'ouie rt sur 1'audition, etc. chap. i. %. x. 

 Paris, 183(5. 



2 K 



