90 GLANDS. 



surface of the lung, whilst their summits are conti- 

 nuous with the bronchial passages. They are sepa- 

 rated by a delicate interstitial lamina of connecting 

 tissue. Their diameter often reaches two-thirds of an 



minute structure of the lungs, Med. Chir. Trans., vol. xxviii. 1845) ; 

 ' infundibul urns' (Kossignol, Recherches sur lastructureintim.edu Poumon 

 de VJiomme, etdes principaux mammiferes, Brussels, 1846) ; ' Halpigliian 

 vesicles' (Moleschott, de MalpigManis Pulmonum vesiculis, Heidelberg, 

 1845) ; and * terminal cavities' (Mandl, Anat. Mivroscop. t. ii. cb. vi.). 7 " 

 To all of these terms the author objects, as not expressing clearly the 

 nature of the structure they are intended to designate ; and after dis- 

 cussing and rejecting them seriatim, proposes, although unwillingly, a 

 new term which, he believes, expresses in a "shorter and more exact 

 manner than any previously used, the particular character and arrange- 

 ment of the portion of the lungs under consideration :" this term is 

 " air-sacs" " The air-sacs are those tubes In which the bronchial rami- 

 fications end ; they are situated at the surface, and throughout all parts 

 of the lung; they are supported externally by the pleura, and within the 

 lung they in part rest, by their extremities or their sides, against the 

 bronchial tubes and branches of the blood-vessels, and they are visible 

 through the transparent coats of the smaller bronchial tubes, as through 

 the pleura. The air-sacs consist of somewhat elongated cavities which 

 communicate with the bronchial ramification by a circular opening, usu- 

 ally smaller than the cavities into which it leads, and which has some- 

 times the appearance of a circular hole in a diaphragm, or as if it had 

 been punched out of a membrane which had originally closed the 

 entrance to the sac; when this is the case the sac dilates suddenly 

 beyond the orifice. The sacs are arranged in groups (usually from six to 

 ten composing a group, p. 144) ; they are placed side by side, and sepa- 

 rated from each other by their membranous walls ; their shape, when 

 properly inflated, or when distended by some material which has set in 

 the sacs, such as gelatine, or a mixture of wax and turpentine, is polygonal ; 

 they approach very nearly to the circular form, but in consequence of 

 their mutual pressure, their parietes become somewhat flattened. They 

 increase somewhat in size as they pass from the bronchial tubes to their 

 fundus, the latter being usually the broadest part of the sac; but they 

 are often found to have an almost uniform diameter throughout. All the 

 sacs pass from the extremity of the bronchial tube towards the circum- 

 ference of the lobule in which they are placed ; they consequently radiate 



