MR. ST. G. MIVART ON THE ANATOMY OF ECHIDNA HYSTRIX. 399 
in the majority of mammals; in Pteropus it is still less in degree, while in some 
Reptilia it disappears altogether, the humerus not only resembling the femur in size 
and shape, but also in the aspect of its proximal artieular surface. This is particularly 
well seen in Chelonians !, in which the correspondence between the humerus and femur 
for the whole length of each is at once evident without the necessity of any real or ima- 
ginary rotation of either bone. 
Putting aside, then, the objections that may be founded on the opposed direction of 
the proximal articular surfaces of the humerus and femur, it is evident that if the cor- 
respondence between the extensor surfaces of those two bones extends to their summits, 
the anterior and posterior borders of the proximal, as well as of the distal, parts of one 
must be serially related to the anterior and posterior borders of the proximal, as well as 
distal, parts of the other. Now when the limbs are placed with their flexor surfaces 
inwards, and the pollex and hallux, radius and tibia forwards, we find, in the humerus, 
two prominences (the two tuberosities), one on the radial side of the bone and projecting 
more or less forwards, the other towards its ulnar side and projecting more or less back- 
wards. Similarly in the femur there are two prominences (the two trochanters), one 
towards the tibial side of the bone and projecting more or less forwards, the other on its 
peroneal side and projecting more or less backwards. In fact it becomes evident that 
the radial (or greater) tuberosity is the homotype of the tibial (or smaller) trochanter, 
and, on the other hand, that the ulnar (or lesser) tuberosity is the homotype of the 
peroneal (or greater) trochanter ?. 
' This relation is disguised in Man and in many animals by the fact that in the fore 
limb the radial tuberosity is large and the ulnar one small, while in the hind limb the 
reverse condition obtains between the trochanters, the tibial one being so much the 
smaller. This decrepancy, however, is not constant. Thus in Galeopithecus the ulnar 
(or lesser) tuberosity very much resembles, both in size and shape, the peroneal (or 
greater) trochanter. In Cholæpus® the peroneal (or lesser) trochanter is relatively as 
large as the radial (or greater) tuberosity, which is not more, perhaps even less, de- 
veloped than is the ulnar (or lesser) tuberosity. 
In Bradypus *, also, the ulnar (or lesser) tuberosity is decidedly larger than the radial 
(or greater) one. 4 
In Pteropus, at least in some species, the condition existing in Man and most verte- 
brates is completely inverted, the ulnar (or lesser) tuberosity and the tibial (or lesser) 
trochanter being more developed than are the radial tuberosity and peroneal trochanter 
respectively. | 
In Birds the true serial relations seem, at first sight, to be somewhat obscured by the 
* See the fine skeleton of Chelydra Temminckii lately added to the Museum of the Royal College of Surgeons. 
* Since this paper was read, I have learned from Professor Huxley that, in 1864, he enunciated at the College of 
Surgeons this inverse relation of the tuberosities and trochanters ; but the fact not being recorded in the only report 
extant of the Hunterian Lectures for that year (at only the last three of which I was present), I had no means whatever 
of becoming acquainted with a fact which had even for a time escaped his memory. 
See no. 2387 a in the Collection of the Royal College of Surgeons. 
See no. 2367 in the same Collection. 
