650 Dr. F. E. Beddard on the Blow-holes and 



nasal region. It comes, so to speak, under the influence o£ 

 the mesethmoid, wliicli is from the first to the end quite 

 median. The oblique course o£ the nasal section of the 

 cartilage gradually straightens to the median position. 



§ Lining Epithelium of Nasal Passages. 



The anterior section of the two nasal passages is lined 

 with a continuous epithelium^ which in all — or, rather, the 

 much greater part of — my sections has become detached 

 from the muscular and connective-tissue walls of these 

 passages. This has also led, as I imagine, to the disappear- 

 ance of some of the sections of the lining epithelium. For 

 during the process of cutting the sections the whole head 

 of the animal had to be unmounted, dealt with further, 

 and re-imbedded in the paraffin. Thus it is difficult to be 

 absolutely certain how far the epithelium, with the characters 

 which I shall immediately describe, extends along those 

 tubes towards the posterior opening into the pharynx. They 

 extend, at any rate, a long way behind the dilatation of the 

 right blow-hole. At first the detached epithelial lining 

 forms a solid rod-like structure in the sections with a slight 

 swelling at each end, giving to it here a club-like form. It 

 is solid throughout and has no central cavity. There is, 

 however, a differentiation into a cortical layer, so to speak, 

 and a medullary layer. The former is more densely stained, 

 and is composed of columnar cells. The central part is 

 formed of non-columnar cells less stained. Later on a 

 vacuity appears in the two club-shaped extremities referred 

 to above, and later still the epithelium clings to the actual 

 wall of the nasal passage, and the central layer of the fused 

 epithelium of the whole periphery has disappeared. 



The state of affairs visible in this foetus evidently leads to 

 the complete occlusion of the nostrils in the anterior part, 

 and is precisely what is to be found in the developing 

 Apteryx^ according to the late Prof. T. J. Parker *. 



§ Dilator and Occlusor Muscles of Nasal Passages. 



These muscles are very distinct, especially those which 

 dilate the passages ; this conspicuous appearance of the 

 dilator fibres is due to the fact that in transverse section 

 they are seen throughout their whole length radiating out 



* " Observations on the Anatomy and Development of Apteryx,'^ 

 Phil. Trans, vol. 182 b, 1891, p. 25. 



