. Chordate morphology. Morphology (Animals); Chordata. ventral bronchi clavicular air sac anterior thoracic air sac ventral bronchi' lateral bronchi dorsal bronch posterior thoracic air sac abdominal air sac dorsal ventral. recurrent bronchi anterior thoracic air sac lateral bronchi Figure 9-30. Semidiagrommotic lungs and air sacs of the bird. A, dorsolateral view of right lung of 9-day-old chick foetus; B, adult system in ventral view. (A after Witschi, 1956) freely into the body cavity. Among anurans the body sur- face has an important accessory respiratory function. Embryological developmen
. Chordate morphology. Morphology (Animals); Chordata. ventral bronchi clavicular air sac anterior thoracic air sac ventral bronchi' lateral bronchi dorsal bronch posterior thoracic air sac abdominal air sac dorsal ventral. recurrent bronchi anterior thoracic air sac lateral bronchi Figure 9-30. Semidiagrommotic lungs and air sacs of the bird. A, dorsolateral view of right lung of 9-day-old chick foetus; B, adult system in ventral view. (A after Witschi, 1956) freely into the body cavity. Among anurans the body sur- face has an important accessory respiratory function. Embryological development in reptiles and amphibians The lungs arise from the floor of the pharynx as in the higher forms. First a laryngotracheal groove appears in the floor of the pharynx, and from this paired outgrowths arise. The medial groove is later converted into the trachea, and the bilateral outgrowths become the lungs. The alligator or bird parallels the mammal in the course of the development of the lung buds, which branch succes- sively in the formation of the organ (Figure 9-31). In the bird the dorsal and ventral bronchi branch repeatedly to form the parabronchi; those of the dorsal and ventral bronchi meet midway between these two series along an oblique plane and fuse. In this way, what were blind-end- ing tubules come to form loops. In most reptiles and amphi- bians the lung buds merely expand, with a few knob-like diverticula, to form the definitive lung. In the reptile a variety of membranes form an association with the lungs, and occasionally the lungs are nearly cut off from connection with the abdominal cavity, as is the case in Tupinambis. However, a diaphragm as such is never formed. In the amphibian there is no attempt to isolate the lungs from the remainder of the body cavity. From their position and paired origin, it is generally as- sumed that the lungs represent a posterior set of gill pouches. In the case oi Hypogeophis, there are eight pairs of pharyngeal pouches; the m
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