. Evolution and disease . an Ears with so-called supernumerary auricles. numbered I to VI in fig. 96, and it is by the coalescence ofthese six tubercles that the pinna is formed. The detailsof their fusion are briefly these:—tubercles I and Vunite across the fissure and form tragus and antitragus,the gap, or notch, between them is represented in theadult as the fissura intertragicum ; tubercle VI uniteswith these to form the lobule; tubercle II forms thehelix, whilst III lengthens out and forms the conchalrim and the tail, or cauda helicis, whilst the tuberclemarked IV becomes the antihelix. T
. Evolution and disease . an Ears with so-called supernumerary auricles. numbered I to VI in fig. 96, and it is by the coalescence ofthese six tubercles that the pinna is formed. The detailsof their fusion are briefly these:—tubercles I and Vunite across the fissure and form tragus and antitragus,the gap, or notch, between them is represented in theadult as the fissura intertragicum ; tubercle VI uniteswith these to form the lobule; tubercle II forms thehelix, whilst III lengthens out and forms the conchalrim and the tail, or cauda helicis, whilst the tuberclemarked IV becomes the antihelix. These facts explain readily enough the mode of origin TJiANSMISSION OF MALFORMATIONS. i8i of the various congenital defects of the pinna. Thus afistula in the helix results from incomplete coalescenceof the tubercles II and III, whilst a fistula in the lobulerepresents a gap between the tubercles I, V, and VI. Thefurrow in the lobule is a fault where the lobule comesinto relation with the tail of the helix. Should any of. Fig. 96.—a, the six tubercles surrounding the first cleft ; B, anintermediate stage in the coalescence of the tubercles. C, astill later stage. (After His.) the tubercles fuse superficially and leave an intermediatespace, this may subsequently dilate and form what isknown as a dermoid cyst—that is, a tumour with a centralcavity lined with skin resembling that covering thepinna. These facts are of some importance because, with an 18 2 E VOL UTION AND VISE A SE. imperfect knowledge of the mode of origin of the pinna,these conditions might admit of a somewhat differentinterpretation. For example, the congenital hole in thelobule could on superficial examination be interpretedas the result of piercing the lobe of the ear for thesuspension of ornaments, but the details of the develop-ment of the pinna offer a much more satisfactoryexplanation of the phenomenon. A careful analysis ofthe facts at our disposal strongly points to the conclusionthat defects due to
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectabnormalitieshuman
