. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. RESPIRATORY ORGANS- 31 phibia. These bronchioles may be as large as, or even larger than, the smaller bronchi; but they differ from them in the ab- sence of cartilage and glands in the wall, in the absence (usually) of cilia on the internal surface, and in the existence of alveoli arising directly from their walls. Besides the lobulation implied by this branching of the respira- tory ducts, the lungs may also be divided into lobes, varying in number, clearly recognizable from the exterior. The lungs of birds are pe- culiar i
. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. RESPIRATORY ORGANS- 31 phibia. These bronchioles may be as large as, or even larger than, the smaller bronchi; but they differ from them in the ab- sence of cartilage and glands in the wall, in the absence (usually) of cilia on the internal surface, and in the existence of alveoli arising directly from their walls. Besides the lobulation implied by this branching of the respira- tory ducts, the lungs may also be divided into lobes, varying in number, clearly recognizable from the exterior. The lungs of birds are pe- culiar in several respects. The primary bronchus, after entering the lung, continues along the ventral surface to near the end of the organ. Near its entrance it gives off several lateral bron- chi, which also course along the ventral surface, and extend onto its sides. The primary bron- chus also gives off from its dor- sal surface a larger number of secondary bronchi, which extend through to the dorsal surface. From these dorsal and lateral bronchi arise numbers of slen- der tubes, the so-called lung- pipes or parabronchi, which are to be regarded as modified bron- chioles, since they have similar walls, and since they connect with the infundibula. They differ, however, from the bron- chioles of the mammals in that they unite or anastomose fre- quently with each other, thus converting the whole lung into a network of tubes (compare the condition in chameleon, above). In the embryonic avian lung thin-walled sacs arise from the outer surface of the lung. These air sacs increase in size, and ex- tend themselves in every direction, — into the abdominal cavity, where they enter between the viscera, in between the muscles, and beneath the skin ; they enter many of the bones (especially. Fig. 34. Diagram of lung struc- ture in man. B, bronchi; BL, bronchioles; A, alveolar duct; /, infundibulum, surrounded by alveoli. Only a very few bronchi Please note that these images are extrac
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