100 BULLETIN UNITED STATES GEOLOGICAL SURVEY. [Yol.YT. 



bral ribs bear a movably articulated epipleural appendage, eacli resting 

 in a shallow cavity designed for it upon the posterior borders. They 

 leave the rib at right angles, but soon turn upward with a varying ab- 

 ruptness. The appendage of the first rib is situated lowest of any on 

 its rib, that of the last the highest ; the facets of the others are found 

 in the line joining those of the first and last. They all make acute 

 angles with the bodies of the ribs to which each belong, above their points 

 of insertion. The angle made by the last is the least, and it increases to 

 the last. The epipleurals of the leading i)leurapophyses are the widest 

 and generally the longest (the one on the second rib in a skeleton of 

 this bird now before me is as wide as the rib at the point from where it 

 starts), the one on the last rib being always -the smallest. 



Clubbed at their sui^erior extremities, each one overlaps the rib behind 

 it, and in this manner add stability to the thoracic parietes, which is 

 undoubtedly the function these little scale-like bones were intended to 

 fulfil. The hcemj^apoliyses connect the vertebral ribs with the ster- 

 num. There are six of them, one articulating with each vertebral rib 

 and having a concave facet to receive it, while the last meets the sacral 

 rib above and articulates with the posterior border of tlie fifth below. 

 The first one is the shortest and most slender of all ; the fifth is the 

 longest. With the exception of the last, their superior ends are enlarged 

 and compressed from side to side, while below their middles they be- 

 come smaller ; then turning upon themselves, suddenly enlarge again, so 

 as to be flattened from before backwards, when each terminates by a 

 transverse articular facet for articulation with the hcemal spine. Quite 

 an interspace exists between their points of contact with the sternum. 

 They all make a gentle curve upwards just before meeting their respect- 

 ive ribs. The hsemajDophysis that articulates with the sacral rib is in- 

 serted in a long, shallow groove on the posterior border of the sternal 

 rib that articulates with the last dorsal pleurapophysis, but does not 

 meet the sternum — simjjly terminating in a fine point on the posterior 

 border of the sternal rib mentioned. From before backwards the ster- 

 nal ribs make a gradually decreasing obtuse angle with the vertebral 

 ribs, while the angle they make with the sternum is a gradually increas- 

 ing acute from the fifth to the first. On the anterior surfaces of their 

 exx)anded sternal ends are to be found on each a minute pneumatic fora- 

 men or two. The anterior third of the lateral borders of the sternum is 

 the space allotted for the insertion of these bones. 



The Burrowing Owl being a bird not possessed of any considerable 

 power of flight, a circumstance arising from the life it was destined to 

 lead, or the necessity of having that flight ever long sustained, we would 

 naturally expect to find, in the course of a study of its anatomy, those 

 characteristic modifications of the various systems which pertain to spe- 

 cies of the class in which that gift has always been a secondary consid- 

 eration. JSTor are we disappointed in this expectation, for a single 

 glance at the size of the sternum of this Owl, when compared with the 



