Bronchial Diverticula in Blarina brevicuada

Abstract

A cursory examination of the thoracic viscera of the short-tailed shrew, Blarina brevicauda (Say), revealed a pair of extrapulmonary bronchial diverticula emerging from the dorsal caudal margin of the right posterior lobe of the lung. These received only passive interest as anomalous developments peculiar to the individual, until their presence in subsequently dissected specimens suggested that they might be a variation characteristic of the species. Though distal extrapulmonary extensions of the bronchi occur in birds and certain reptiles, where they function as vital or ancillary components of the respiratory system, no homologous structures have been described as a constant anatomical entity in mammalian lungs. By virtue of size and location, the bronchial diverticula in the shrew were non-functional in any respiratory capacity, and the existence of a more subtle selective factor was suspected to be responsible for their perpetuation in the heredity of the species. Therefore, in addition to a description of the diverticula, this study included an attempt to derive a functional apology for their occurrence from the histological and morphological picture presented by the lung of Blarina with regard to comparative evidence. The diverticula were found in all of ninety-four short-tailed shrews taken in Tolland Co., Connecticut. However, to ascertain if they were a universal possession of the species, a series geographically indicative of the population was necessary. The range of Blarina brevicauda , inclusive of several subspecies, covers all of eastern United States, extending from southeastern Canada to Florida, and west of the Mississippi as far as Nebraska. Through the courtesy of Dr. W. H. Burt, formalin-preserved specimens representing the following subspecies and locations were obtained from the University of Michigan Museum of Zoology: one B. brevicauda brevicauda , Ontario, Wellington Co.; one B. brevicauda brevicauda , Maine, Franklin Co.; five B. brevicauda brevicauda , New Hampshire; …