550 



ORGAN OF HEARING. 



and upwards. In the dry bone it is wide 

 enough to admit the end of a quill stripped of 

 its feathery part, about one-twelfth of an inch 

 thick. In the recent state, when lined by its 

 mucous membrane, it is very much narrower. 



The cartilaginous and membraneous portion 

 of the Eustachutn tube, pars cartilagineaetmem'- 

 branacea tub<e Eustachii. In the skull it is ob- 

 served that the osseous part of the Eustachian 

 tube is continuous with a sort of gutter which 

 is formed by the outer and anterior side of the 

 petrous bone, and the posterior inner and lower 

 margin of the great wing of the sphenoid bone. 

 To this gutter the external wall of that part of 

 the Eustachian tube under consideration, which 

 is partly cartilaginous and partly fibre-membra- 

 neous, corresponds at its tympanic extremity; 

 towards the guttural orifice of the tube, the 

 membraneous wall is applied against the circum- 

 flex muscle of the palate. The inner, and also 

 the upper wall of this portion of the Eustachian 

 tube, is formed of a grooved cartilaginous la- 

 mina of a triangular form, fixed by dense cel- 

 lular tissue to the irregular extremity of the 

 osseous portion, to the apex of the petrous 

 bone, and to the root of the inner plate of the 

 pterygoid process of the sphenoid. At the 

 guttural orifice of the Eustachian tube, it forms 

 a semilunar prominence with its convexity 

 turned upwards and backwards. The cartila- 

 ginous plate of the outer wall does not extend 

 to the mouth of the tube, but only fills up that 

 place where the outer wall of the bony groove 

 above-mentioned as continuous with the osseous 

 part of the Eustachian tube is defective, that is, 

 from before the foramen spinosum of the sphe- 

 noid to the scaphoid fossa at the root of the in- 

 ner plate of the pterygoid process. 



The cartilaginous and membraneous portion 

 of the Eustachian tube is about one inch long. 

 Being compressed from within outwards, a sec- 

 tion of it is an elliptical fissure. From its junc- 

 tion with the osseous portion, it goes on widen- 

 ing, so that the point of junction is the narrow- 

 est part of the tube; in the recent state, about 

 one-thirtieth of an inch in diameter, just suffi- 

 cient to admit a small probe. 



The mouth of the Eustachian tube in the 

 throat forms an oval-shaped fissure, about 

 three-eighths of an inch long, bounded ante- 

 riorly and posteriorly by prominent swollen 

 edges. The fissure is directed obliquely from 

 above downwards, and from before backwards, 

 and is situated at the upper and lateral part of 

 the pharynx behind the soft palate. In refe- 

 rence to the nasal passage, my observation 

 agrees with that of Kramer,* that the lower 

 angle of the guttural orifice of the Eustachian 

 tube lies a very little deeper than the horizontal 

 line of the lowest meatus, whilst the upper 

 angle is a little deeper than the horizontal line 

 of the middle meatus. 



The Eustachian tube is essentially a tegumen- 

 tary canal ; through it atmospherical air is ad- 

 mitted into the tympanum, a condition which, 

 by keeping up an equable pressure on either 

 side of the membrana tympani, and giving free 



* Die Erkenntniss und Heilung der Ohrenkrank- 

 heiten. Berlin, 1836. p. 243. 



scope to the play of the small bones upon each 

 other, is necessary for the perfect exercise of 

 hearing. Its lining membrane is continuous 

 with that of the throat on the one hand, and 

 with that of the tympanum on the other. 

 At the guttural orifice of the tube, it has all the 

 properties of the mucous membrane of the 

 nose and throat ; as it approaches the tympa- 

 num it becomes thinner and finer, until it 

 assumes all the characters of the fibro-mucous 

 lining of the tympanum. Within the osseous 

 portion of the tube, it no longer presents any of 

 the mucous glands which are found in the 

 mucous membrane of the prominent edges of 

 the guttural orifice, and in that lining the carti- 

 laginous and membraneous portion mucous 

 glands, which perform so important a part in 

 the economy, and particularly the morbid states, 

 of the Eustachian tube and apparatus of hear- 

 ing generally. 



Fig. 252. 



The two muscles of the small bones, and the Eusta- 

 chian tube. (From Soemmerring . ) 



a. b. c. d. Eustachian tube ; e. muscle of the mal- 

 leus ; f. the muscle of the stapes. 



2. The external ear, including the auditory 

 passage. 



A. The auricle or the ear, (auricula s. pin- 

 na,) Fr. pavilion de Voreille; Germ, das Ohr. 

 The human auricle, as is known, presents on 

 the surface directed outwards, prominences 

 bounding gutter-like depressions, which wind 

 like a maze in different directions; but all lead 

 at last into the auditory passage. Considered 

 in a general way, the surface directed outwards 

 is concave. The surface turned towards the 

 side of the head is, on the contrary, generally 

 speaking, convex, but it fs depressed at the 

 places corresponding to the elevations on the 

 outer surface, and more elevated where the de- 

 pressions are. 



The hem-like fold of the edge of the ear all 

 round is called helix. The eminence within 

 the helix is called anthelix, and the gutter-like 

 depression between the two is called the navi- 

 cular fossa. At its upper extremity the anthe- 

 lix divides into two branches, between which is 

 a triangular depression czlledfossa innominata. 

 The lower extremity of the anthelix runs into 

 a projection called antitragus, opposite which, 

 and under the anterior part of the helix, is a 

 broad projecting plate called tragus, which 

 lies over the entrance of the auditory passage 



