74 THE LUNGS, BY FRANZ EILHARD SCHULZE. 



wall of the pulmonary sac towards the bronchial orifice, and 

 which, like other parts of the pulmonary wall, are themselves 

 beset with smaller ridges circumscribing alveoli. 



In the Chelonia such septa occur in greater numbers, 

 traversing the whole cavity, and fusing completely with the 

 tubular prolongation of the bronchus as it projects into this 

 cavity; so that each lung is divided into a number of contiguous 

 csecal sacculi, usually arranged in two series, which no longer 

 communicate with each other, but are accessible only through 

 the prolongation of the bronchus. 



The alveolar parenchyma covering the inner walls of these 

 several segments of the lung exhibits a similar but rather 

 more complicated structure than in Snakes. As in them, the 

 main septa are here also not smooth-walled, but support on 

 their lateral surfaces smaller septa arranged in a plexiform 

 manner ; these again have others, and so on. 



Finally, in the Crocodile, by a still further development and 

 complication of the alveolar parenchyma in the same direction, 

 the above-described sac-like main air passages become con- 

 stricted into the form of rounded tubuli, without, however, the 

 actual formation of true solid- walled bronchia, such as are found 

 in Mammals. 



Throughout theReptilia and Amphibia the histological matrix 

 of the whole pulmonary tissue consists of fibrous connective 

 tissue intermingled with a plexus of fine elastic fibres, contain- 

 ing in many instances, as in Salamandra maculata and nume- 

 rous frogs, a large quantity of pigment cells filled with black 

 granular material. In some animals, however, as the Chameleon, 

 Scincus, Testudo grseca,Emys europseus, and Coluber natrix, but 

 few pigment cells are present, whilst in others, as the Lacerta 

 agilis and Alligator sclerops, they are altogether absent. 



The continuation of the bronchus penetrating to a greater or 

 less depth into the lung, and forming either a partially grooved 

 tube, as in Ophidia, or a straight tube perforated with rounded 

 openings, as in Chelonia, or a ramified tube, as in Crocodiles, pre- 

 sents in its otherwise fibrous wall, rings composed of hyaline 

 cartilage, homogeneous in structure, and frequently connected 

 by communicating laminae, the opposite sharp borders of which 

 are united by a. tense web of longitudinal elastic fibres. 



