646 



perienced person, when a fragment, however small, is examined by 

 the microscope. 



When the bronchial tubes have reached their penultimate termi- 

 nations, the coats which form their perimeters split, as it were, into 

 two layers. The outer of these, which is tougher, thicker, and more 

 fibrous, expands and encloses an ultimate portion of the parenchyma. 

 To these portions of the lung the name of * leaflets ' is given in this 

 treatise. The outer coat of the bronchial tube, by being spread out 

 in the leaflets, becomes continuous with the general parenchyma of the 

 lungs. The inner portion of the tube immediately divides into nu- 

 merous minute tubes, to which the name of ' pedicels * is now given. 



Each of the pedicels goes to a different leaflet, but each leaflet 

 receives several pedicels from different terminal bronchial tubes. 



A minute anastomosis is thereby established between the termina- 

 tions of the different bronchial tubes, through the leaflets. On 

 entering the leaflet, each pedicel splits up into processes which ex- 

 tend to the internal perimeter of the leaflet, and by intersections with 

 similar processes derived from the other pedicels, divide the interior 

 into compartments called c air-cells.' 



Each leaflet is, to a considerable extent, divided from those which 

 surround it by sulci, but it is continuous in structure with them by 

 certain parts of its base, in which it is in contact with them and 

 adherent. 



On the surface of the lungs these leaflets give the appearance of 

 bodies of a somewhat quadrilateral shape. 



The interior of all the bronchial tubes is marked with 'rugae,' and 

 these rugae show the direction of the bundles of longitudinal con- 

 tractile fibres, which are placed immediately beneath the mucous 

 membrane. These longitudinal fibres are surrounded by circular 

 ones, and it is by the contraction of these latter that the rugae are 

 formed. When the bronchial tubes have been kept distended, the 

 rugae are not present ; the mucous membrane is then perfectly smooth. 



There are no such things as f alveoli ' belonging to the tube. 



The bronchial artery supplies the following structures : 



I. The successive layers of cellular tissue, the lymphatic glands, 

 coats of the pulmonary vessels, neurilemma, &c. 



II. The fibre-cartilaginous and fibrous portion of the bronchial 

 tubes ; some exceedingly minute capillaries, derived from these, ex- 



