578 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 



and knobbed al the sternal extremity, where the cross-section would be 

 decidedly triangular. 



The scapula is about 1.75 ruches long l>y 0.90 broad at the widest part, 

 and presents numerous well-marked features. The general contour is that of 

 an inequilateral triangle with the postero- superior corner rounded off, and the 

 anterior angle produced into a neck. The lower border, which is much the 

 longest, is nearly straight; the posterior curves gently upward and forward, 

 and is as long as the superior, which, at first convex, then curves with con- 

 cave outline to the superior border of the glenoid. The ventral surface is 

 uneven, being marked by a median line of impression, indicating the root of 

 the spine on the opposite face, and by two radiating ridges on either side of the 

 median line; while there are also two other ridges, one running the whole 

 length of the superior border, the other marking a small part of the inferior 

 border near the postero-inferior angle. Thus the bed of the subscapularis 

 muscle is divided by these four ridges into three compartments. The dorsum 

 of the blade is quite smooth and nearly flat; the very prominent spine, run- 

 ning the whole length of the bone, divides this surface into an upper, broader 

 but shorter, and an under, longer but narrow, portion for the supraspinatus 

 and infraspinatus muscles respectively. The plate of the spine is perpendic- 

 ular to the body of the bone ; its free edge is strongly convex throughout, the 

 height of the spine at its middle being nearly as great as at its acromial end, 

 and somewhat sinuous from deflection of the plane of the spine out of the 

 perpendicular; the greatest height is about 0.50, or more than half the 

 greatest width of the bone. At its fore end, the spine develops a well 

 marked prominent acromial process, reaching forward and upward, the plane 

 of which is twisted nearly at right angles with that of the rest of the spine. 

 The fore edge of the spine is a strongly concave line running from the neck 

 of the scapula to the apex of the acromion. The neck of the bone is well 

 marked ; the lower part of the shallow glenoid fossa is nearly circular, but 

 the articular surface is much produced above, giving a somewhat pyriform 

 shape to the outline of the whole cavity. There is a conspicuous coracoid, 

 projecting hook-like from the supero-interior corner of the glenoid. 



Bones of the fore limb. — The humerus, about 1.75 long, is a stout bone, 

 straight on the whole, but with numerous salient points and ridges. The 

 articular head, rather less than hemispherical, and not circular in section, 

 being longer than wide, is sunken between prominent greater and lesser 



