HAPLODONTIDiS— LIMB BONES OF FIAPLODON RUFUS. 579 



trochanteric tuberosities, without appreciable neck. There is a strong deltoid 

 ridge, running down from the greater or external tuberosity, and terminating in 

 a stout, prominent, roughened tubercle just above the middle of the shaft, from 

 which a slighter ridge runs down to the inner side of the ulnar articular 

 facet. Below, the bone flattens and widens laterally to a breadth of 0.60. 

 From the external condyle, a sharp ridge curves backward and upward to 

 subside on the shaft at the middle of the latter; the inner condyle project- 

 ing laterally much farther from the articular facet than the outer one, though 

 no such condylar ridge is prolonged up the shaft of the bone. This condyle 

 is perforated with a large canal, oval in section, formed by a bony trabecule 

 thrown across in front. The ulnar portion of the articular facet, lying in the 

 main axis of the bone, constitutes, as usual, a simple ginglymoid joint, being 

 very convex antero-posteriorly, concave in the opposite direction ; its inner 

 edge is ridged, its outer continuous with the radial articular surface, which 

 latter is convex in all directions. Just above the joint, at the back of the 

 bone, there is the usual pit for the reception of a process of the ulna; but 

 the bone is not here perforate, though very thin. The position of the articular 

 surfaces allows strong flexion of the forearm, but scarcely permits complete 

 extension. 



The ulna, two inches or more long, presents a strong olecranon extend- 

 ing back of the joint to a distance greater than the length of the articular 

 surface. The latter is a semicircular nick, very oblique in position with refer- 

 ence to the axis of the bone ; the facet for the articulation of the radius is 

 distinct. On its inner face, the shaft is deeply grooved for the reception of 

 the radius, which lies in close apposition with the ulna for the whole of its 

 own length ; but the ulnar groove continues up beyond the head of the radius. 

 On the inner face of the bone, a somewhat similar groove runs from the side 

 of the olecranon past the joint, but soon becomes obsolete. The ulna ends 

 below with a simple conical extremity, which takes but little share in the 

 formation of the wrist-joint. 



The radius, about 1.G0 long, lies close to the ulna its whole length ; the 

 shaft is much bent outward; the head is oval in section, with a cupped 

 facet for humeral articulation, and smooth, convex, lateral facet for the ulnar 

 joint. The tubercle for insertion of the biceps is recognizable. The lower 

 extremity is enlarged, bearing an oval facet, the outer corner of which is 

 produced as a slight process. Notwithstanding the restriction of motion 



