354 MANUAL OF HISTOLOGY. 



no difference between the two portions, except that the carti- 

 lage is replaced by bone. 



The ear of a new-born -child can be easily removed with the 

 cartilaginous part of the meatus, and when hardened in Miil- 

 ler's fluid and afterward in alcohol, and imbedded in paraffine 

 or hardened liver, furnishes sections which, when colored with 

 hsematoxylon, show the different relations very clearly. The 

 osseous portion must first be decalcified by allowing the bone 

 to hang freely in a weak (i per cent.) solution of chromic 

 acid, often renewed, during several months. The specimens 

 are then to be well washed, hardened in alcohol, and prepared 

 as above. 



At the inner end of the external meatus, and separating it 

 from the middle ear, is stretched the membrana tympani. The 

 tympanic ring, with the membrane attached to it, is to be care- 

 fully separated from the surrounding parts by means of bone- 

 scissors, and placed for five to fifteen minutes in a weak solu- 

 tion (two to five per cent.) of formic or acetic acid. It should 

 then be well washed in distilled water, and the external layer 

 of epithelium removed by a camel' s-hair brush, and finally 

 stained with hsemotoxylon and mounted in glycerine. In spe- 

 cimens thus prepared there are to be distinguished three lay- 

 ers, viz.: an external or cuticular layer, a middle or fibrous 

 layer (membrana propria), and an internal or mucous layer. 



The cuticular layer is composed of simple pavement-epithe- 

 lium, without glands or hairs. It is thickest at the periphery, 

 and over the'handle of the hammer, and along its edge. 



The fibrous layer (membrana propria) consists of two sets 

 of flattened, spindle-shaped fibres, with long, thin connective- 

 tissue corpuscles imbedded in them, and which have a close 

 analogy with the fibres of tendons. The outer series, lying 

 directly beneath the cutis, radiates from the handle of the 

 hammer toward the periphery, while the inner series circles 

 about the handle. At the periphery the two series interlace 

 with each other and with a few fibres coming from the cuticu- 

 lar and mucous layers to form the so-called tendinous ring, in 

 which are also to be found a few scattered cartilage-cells. This 

 ring is joined to the annulus tympanicus by a thin periosteum. 

 (The handle of the hammer is joined to the membrana tympani 

 by a cartilaginous formation which stands in close relation to 

 the membrana propria. This is a shallow groove of hyaline 



