HEART. 



577 



1. The vestibule is the essential part of the 

 organ. It detects the presence and intensity 

 of sound, and especially of those sounds con- 

 veyed through the external ear and tympanum. 



2. The cochlea, lying in immediate connec- 

 tion with the bone, receives those sounds which 

 are propagated through the bones of the head. 

 According to Kerner it is the medium of the 

 perception of the timbre or quality of sounds.* 



3 . Of the function of the semicircular canals 

 we know nothing. That they aid in forming a 

 judgment of the direction of sounds is conjec- 

 tured by Autenrieth and Kerner, and more re- 

 cently by Wheatstone. 



4. The tympanum and its membrane render 

 the internal ear independent of atmospheric 

 vicissitudes, and the former affords a non-reci- 

 procating cavity for the free vibration of the 

 latter, as well as of the chain of ossicles. 



5. The chain of ossicles acts as a conductor 

 of vibrations from the membrana tympani to 

 the fenestra ovalis, and under the influence of 

 the muscles regulates the tension of the mem- 

 brana tympani, as well a? the membrane of the 

 fenestra rotunda, so as to protect the ear against 

 the effects of sounds of great intensity. 



6. The external ear and meatus are con- 

 ductors of vibrations ; the former in some de- 

 gree collects them as a hearing-trumpet would 

 do, and probably assists in enabling us to judge 

 of the direction of sounds.f 



(R. B. Todd.) 



HEART (in anatomy). Gr. xea, xagjVa; 

 Lat. cor; Fr. cceur ; Germ. Herz ; Ital. cuore. 

 The movement of nutritious juices through the 

 texture or textures of which an organized body 

 is composed, is a fundamental law in Physio- 

 logy. In proportion as the vital actions become 

 more complex and energetic, the more a rapid 

 and certain circulation of these fluids, which 

 is intimately connected with this condition, 

 becomes indispensable, and for this purpose 

 we have a pulsatory sac or sacs, called hearts, 

 superadded to the circulatory apparatus. Ano- 

 ther invariable concomitant of this energetic 

 manifestation of the vital phenomena is the 

 more perfect exposure of the nutritious fluids 

 to the atmospheric air, and this, combined with 



* Muller, who seems to regard the cochlea as an 

 apparatus for distinguishing the pitch of notes, 

 accounts for its peculiar form thus: He supposes 

 it an organ in which the separate parts of the nerve 

 may be exposed to excitation ; for this purpose all 

 the finest fibres of the nerve lie exposed to the in- 

 fluence of the sound-conducting medium, and that 

 it has assumed the spiral form in order that the 

 nerves may be arranged in the most convenient 

 manner and within the smallest space . See his Frag- 

 ment on the sense of hearing appended to his work, 

 Zur vergleichenden Physiologic des Gesichtssinnes. 



t Much remains to be done to determine the true 

 means by which we judge of the direction of sound. 

 The reader who may be interested on the subject 

 will find some valuable observations and experi- 

 ments in Autenrieth and Kerner's paper already 

 quoted, Mr. Gough's paper in the Manchester 

 Memoirs, vol. v., new series, and one by Venturi 

 in Voigt's Magazin f. d. Neueste aus der Physik. 

 Mr. Wheatstone's views are very briefly stated in 

 Dr. Elliotson's Physiology. 



VOL. II. 



the dissimilar media in which different animals 

 live and move, necessitates very important 

 modifications in the number, position, and 

 structure of these pulsatory sacs. These hearts 

 were until lately supposed to be exclusively 

 confined to the sanguiferous vessels, but Muller 

 and Panizza have discovered distinct pulsating 

 sacs placed upon the lymphatic vessels in 

 several of the reptile tribe, and these may be 

 considered lymphatic hearts. 



In the lowest organized plants, as the Fungi, 

 Algae, &c. and in the lower classes of animals, 

 as the Polypi, Actiniae, and a great part of the 

 intestinal worms, the nutritious fluids are trans- 

 mitted through their substance without any 

 distinct canals or tubes ; while in the higher 

 classes of plants, and in the Medusae, &c. 

 among animals, vessels are present, but these 

 are unprovided with any pulsatory cavities. In 

 the articulated animals generally, the vessels 

 are still without any pulsatory cavities; but to 

 make up for the deficiency, the dorsal vessel 

 itself has a distinct movement of contraction 

 and relaxation. Various pulsatory dilatations 

 are placed upon the vascular system of the 

 common worm (Lumbricus terrestris) ; one or 

 two upon the vascular system of the Holo- 

 thuria ; and one in the Talpa cristata, where 

 the dorsal vessel is reflected upon itself at the 

 posterior extremity of the body to become con- 

 tinuous with an analogous ventral vessel ; all 

 of which may be considered as rudimentary 

 hearts. 



As we rise in the scale of animals, we find 

 that the heart consists of two distinct portions 

 of a stronger and more muscular cavity called 

 a ventricle, and of a weaker and less muscular 

 cavity called an auricle. The latter not only 

 serves as a kind of reservoir to the former, but 

 also, by the contraction of its muscular fibres, 

 drives the blood into it. This heart is placed 

 within a sac or pericardium, and possesses 

 valves to prevent the regurgitation of the blood 

 from the ventricle into the auricle, and from 

 the aorta back again into the ventricle. This 

 may be considered as a perfect single heart. 

 This single heart in some of the Mollusca and 

 in Fishes which have a double circulation, 

 propels the blood not only through the lungs, 

 but also through the body. In the Batrachian 

 Reptiles, as in the Frog, though the circulation 

 is single, the heart becomes more complicated ; 

 for instead of a single auricle we have two, one 

 of which receives the blood returning from the 

 respiratory apparatus, the other receives the 

 venous blood of the body. The pulmonic and 

 systemic circulations are here separated as far 

 as the auricles are concerned ; but a single 

 ventricle in which the venous and arterialized 

 blood are intermixed, still continues to propel 

 the sanguineous current both through the lungs 

 and through the body. In the Ophidia or ser- 

 pent tribe the heart possesses the same number 

 of cavities as in the Batrachian Reptiles ; but 

 we have a still nearer approach to the double 

 circulation in the presence of a rudimentary 

 septum ventriculorum. In some of the Sauria, 

 as the Crocodile, the ventricle is divided by 

 partitions into distinct chambers, which never- 



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