A460 H. G. SEELEY ON A MAMMALIAN FEMUR AND 
shaped outline of the external side of the shaft. The inner border 
of the distal end also expands distally, though not to the same ex- 
tent. It is less perfectly preserved, but was obviously much thicker 
and apparently flattened, and makes the width of the distal end in a 
line with the olecranon pit a trifle over 6 inch. The details of 
the distal articulation are not well seen; but the bone appears to 
have been compressed and rounded, and the extension below the 
olecranon-pit of the condyles is rather less than 5!, inch. ‘The ole- 
cranon-pit is not very deep, and is transversely ovate, placed a little 
obliquely, and nearer to the external than to the internal border of 
the bone. The principal condyle was below the inner half of the 
olecranon depression, and is partly broken away ; but a small second 
condyle appears below its external corner, and between these there 
is a narrow smooth impressed intercondylar area, which extends 
obliquely forward and upward, and indicates the mode of flexure of 
the fore limb. 
The nearest approach to this form of humerus is probably pre- 
sented by some of the Phalangers, though the ridge, which is lateral 
ou the side of the upper part of the shaft, would need to be turned, 
together with the head, through a considerable angle before the two 
forms could be brought into harmony. 
On the oblique inner distal border is the usual supracondylar 
foramen seen in Marsupials and several other orders, which appears 
to have a vertically ovate outline, and to pass obliquely forward and 
downward and very slightly inward; it is placed just above the 
border of the olecranon-pit, and is separated from it by a width of 
jy inch. Its inner border is a narrow arch of bone, which is angular, 
being compressed from the front. 
So far we have compared the humerus as though it were an isolated 
bone; and have ignored the possibility that it might present aftinities 
of the same character as the femur. The difficulties which have pre- 
sented themselves hitherto in its interpretation are :—(1) the con- 
cave anterior or external margin; (2) the ridge running down the 
superior aspect of the bone from the proximal articular head. But 
when our comparisons are turned to the Ornithorhynchus, singularly 
modified as the posterior or internal margin of the bone in that genus 
is, we recognize at once the significance of the characters which have 
hitherto been so difficult to interpret. In no other genus is the an- 
terior concavity of the hone between the proximal and distal ends so 
pronounced as in this Monotreme; and although this right humerus 
presents a form which is more suggestive of a Marsupial in its 
general aspect, yet in these important characters, as well as in the 
outward direction of the articular head, it makes an approximation 
to the Ornithorhynchus which there is no reason for believing to be 
accidental, and every reason to regard as an indication of organic 
grade. It is not impossible that the Stonesfield animal may have 
had burrowing habits ; but it is highly probable that a humerus so 
modified as this must have been connected with a pectoral arch like 
that of a Monotreme in construction, and unlike the ordinary form 
of the arch in placental Mammals or Marsupials. And if any diffi- 
culty should suggest itself in this comparison on the ground of the 
