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The meaning of this variation in distribution of the bronchial artery as found in the horse is not clear.

However, this artery is known to be a nutrient vessel with a distribution primarily to the proximal airways and supportive tissues of the lung.

The alveoli and respiratory bronchioles are primarily diffusing tissues.

Theoretically, they are capable of extracting their required oxygen either from the surrounding air ( Ghoreyeb and Karsner, '13 ) or from pulmonary arterial blood ( Comroe, '58 ).

Therefore, an explanation of this alveolar bronchial artery supply might be the nutritive requirement of an increased amount of supportive tissue, not primarily diffusing in nature, in the region of the alveolus.

If this be true, the possibility exists that an occlusive lesion of the bronchial arteries might cause widespread degeneration of supportive tissue similar to that seen in generalized emphysema.

One would not expect such an event to occur in animals possessing lungs of types 1, or 2.