ORGAN OF II EARING. 



Mil 



of tin- long process. In the incus the first 

 point of otlincatk>o occurs in the longer crus 

 near the body, mid from this point it extends 

 iluni!^ i In- linirtli anil iitili inuntlis, so fur that 

 the uhole is ossified with the exception of the 

 point of the short process. The long crus 

 Mrcki'l always found completely ossified, 

 whilst the short crus was still cartilaginous. 



The stapes is still cartilaginous when ossi- 

 fication has made considerable progress in the 

 other two bones. According to Meckel ossi- 

 fication does not commence at any determinate 

 point of the stipes ; only he never observed it 

 first on the head. According to Rathke there 

 are three particular nuclei, one for each of the 

 sides of the triangle which the stapes repre- 

 sents. 



The opening between the crura of the stapes 

 is at first very inconsiderable, a condition 

 analogous to what is found permanent in the 

 Cetacea, &c. 



The ossicles are not unfrequently irregular 

 in their form, size, and situation. They may 

 even be wanting. The stapes, as it is the last 

 formed, presents the most numerous and most 

 varied malformations ; the malleus the fewest. 

 The stapes has been found, by Tiedemann, 

 as it is ;it first, like a pyramid without any 

 opening ; again, it has been found with but a 

 very small opening, or presenting indeed the 

 crura, but the space between them filled up 

 by a thin plate of bone. Only one crus has 

 been found rising from the middle of the base 

 in the form of a slender pedicle of bone as in 

 the bird, and presenting no trace of an articular 

 cavity for the reception of the lenticular pro- 

 cess of the incus, &c. 



A remarkable circumstance connected with 

 the early formation of the malleus is the 

 existence, as Meckel* first observed, of a 

 straight cartilaginous process, having the 

 shape of a very elongated cone, which ex- 

 tends from the anterior part of the head 

 of the malleus to the place where the two 

 halves of the lower jaw unite in front. The 

 cartilaginous process passes out of the cavity 

 of the tympanum between the petrous bone 

 and tympanic ring. This process, though 

 having much the same situation, must not be 

 confounded with the pruct-fsiu gnicilis. The 

 forimr lies above the latter, and both parts are 

 quite distinct from each other. Moreover the 

 cartilaginous process never ossifies, but dis- 

 appears in the eighth month. Iluschkef has 

 discovered a similar process extending be- 

 tween the short crus of the incus and the supe- 

 rior horn of the hyoid bone through the me- 

 dium of the styloid process. 



Op. cit. torn. iii. p. 199. . 1948. See also 

 Huschko Britriitie zur Physiologic und Natnr- 

 ii htc, p. 48. Taf. li. FIR. 1. Isis von Oken, 

 111:1:). Heft. vii. p. 678. S.rrcs, Aunalcs des 

 Sciinces Natiircllcs, 1827, p. 112. Weber, Hilclc- 

 brandl's Anatomic, 4tc. Ausgabc. Band. iv. p. 47. 

 Kailike, op. cit. p. 122, and Valentin, op. cit. 

 p. 214. 



t Isis von Oken, loc. cit. and Valentin, op. et 

 loc. cit. 



The most interesting irregular formation of 

 the malleus is what appears to be connected 

 in some manner with the above described early 

 <ohiliiii.il of the malleus and incus. Such 

 are related by Hyrtl,* IIeusinger,f and 



2. Of the external etir. The external ear 

 soon disappears in the animal series. It is 

 t part of the apparatus of hearing 

 which makes its appearance in the human 

 embryo. It is very subject to irregular deve- 

 lopment. It is only about the middle of the 

 second month that a trace of it can be ob- 

 served. It is at first merely a slight elevation 

 of the skin, broad above, narrow below. In 

 the middle of this elevation is a longitudinal 

 fissure of the same form, which is narrower 

 and at the same time deeper from above 

 downwards. The prominence soon becomes 

 more elevated and thinner at its posterior part, 

 and projects above the surface of the side 

 of the head, from which circumstance the 

 middle depression is a little exposed. At the 

 same time or soon after, the anterior part of 

 the prominence is found divided into two 

 halves by a transverse fissure running forwards; 

 the inferior half is the antitragus, and the supe- 

 rior the commencement of the helix. At the 

 same time this anterior part of the external ear 

 rises also, and the posterior spreads more out. 

 In the third month the anthelix and tragus are 

 developed ; the concha is not yet perfectly dis- 

 tinct; it is only indicated by the middle de- 

 pression. In the fourth and fifth month the 

 hollow of the concha appears, and is completely 

 formed in the sixth. The lobule is the last part 

 which presents itself. 



The cartilage begins to be formed in the 

 third month, but is developed slowly. To- 

 wards the end of pregnancy, though thicker, 

 harder, and firmer, it is still incomplete. 



The cartilaginous portion of the auditory 

 passage as well as the auricle is at first pro- 

 portionally much smaller than afterwards. The 

 skin lining the auditory passage is softer and 

 thicker than in the adult, and is covered with 

 a thickly set down. In the foetus the auditory 

 passage is rounder, straighter, and shorter than 

 in the adult. 



The auricles may not be formed at all, or 

 their development may be so arrested that they 

 shall be represented merely by unshapely folds 

 of skin with or without cartilage, or they may 

 deviate more or less from their usual form, 

 size, and situation. Imperfect formation of 

 the auricle is frequently accompanied by ab- 

 sence or closure of the auditory passage. Pro- 

 fessor Samuel Cooper mentions the case 

 of a child in which there was not the slightest 

 trace either of external ear or auditory passage. 



Op. et loc. cit. 



t Specimen mala; conformations organorum 

 auditus hum;) iii rarissimum et mcinoralu ilignis- 

 siimim, cum tribus tabulis ari incisis. Jcnae, 

 1824. 



J Bcschreibunp: der pathologischcn IVaparatc, 

 writhe in der kbniglichen anatomic-Inn Anstalt 

 zu \\ iirzburg auf bcwahit vvcrdtn. Giessen, 1824. 



2 t 



