606 GEOLOGICAL SURVEY OF THE TERRITORIES. 
the commissure between neck and tubercle, posteriorly. All the verte- 
bral ribs bear a movably articulated epipleural appendage, each 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 theribs 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 pleurapophyses 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 superior extremities, each one overlaps the rib behind 
it, and in this manner add stability to the thoracic parietes, which is un- 
doubtedly one of the functions these little scale-like bones were intended 
to fulfill. The hemapophyses connect the vertebral ribs with the sternum. 
There are six of them, one articulating with each vertebral rib and hav- 
ing a concave facet to receive it, while the last meets the sacral rib 
above and articulates with the posterior border of the fifth below. The 
first one is the shortest the most slender of all; the fifth is the long- 
est. 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 hemal 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 hemapophysis 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—simply 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 
expanded 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 
iead, or the necessity of having that flight ever long sustained, we would 
naturaliy 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. Nor are we disappointed in this expectation, for a single 
glance at the size of the sternum of this Owl, when compared with the 
remainder of its skeleton with regard to areas for muscular attach- 
ments, reveals to us the disproportion of the surface supplied by that 
bone for the attachment of the pectorals. That its dimensions are rel- 
atively contracted is proved by actual, comparative, and proportional 
measurements of the bones with other species of its family, individvals 
of which, at the best, are not noted for their powers of flight, and con- 
_ sequently the sternum does not present so prominent a feature of 
the skeleton as it does in other species of the Class Aves where vigor- 
ous flight is habitual. Life-size figures of this bone, viewed from the 
