1901.] AFFINITIES OF TJDEIfODON. 177 



little to the outside of the middle line ; while to the inside of the 

 great trochanter is a distinct but shallow concavity. On tbe pos- 

 terior side of the bone there is a fairly deep concavity below the 

 head and on the inner side of the small trochanter. On the outer 

 edge of the posterior side there runs down, from a little below tbe 

 great trochanter to beyond the middle of the shaft, a small sharp 

 backwardly directed ridge. In the middle of the shaft a section is 

 almost oval, showing a small but distinct medullary cavity. The 

 lower end of the femur resembles very considerably the lower part 

 of the bone in Echidna or Ornitliorhynchus. The condyles are small 

 and rather widely apart, and, as in the Monotremes, the whole lower 

 end of the femur is much flatter than in the Eutherians. From the 

 neighbourhood of the inner condyle an oblique ridge runs upwards 

 and outwards towards the outer side of the middle of the shaft, 

 apparently corresponding to the oblique ridge on the back of the 

 lower end of the femur of Echidna. 



In the skeleton of Udenodon haini (spec. 4) both femora are 

 shown but in rather bad preservation, having been much crushed. 

 The chief differences in this species are in the bone being propor- 

 tionally stronger, in the greater development of the great trochanter, 

 and in tbe small trochanter being less marked. 



Tihia and Fibula. 



In the skeleton of Udenodon gracilis (PI. XVI.) both tibiae and 

 fibulae are shown, but those of the left leg are not well displayed, 

 and those of the right only show the posterior surface and have 

 been slightly injured in clearing off the matrix. 



The tibia (tb. Plate XVII. fig. 5) is considerably shorter than the 

 femur, and resembles closely the tibia in Echidna. It is a moder- 

 ately straight bone with a large flat head, a shaft tapering down to 

 between the middle and lower thirds, and a distal end moderately 

 dilated and with an oblique articular surface. It has a distinct 

 though small medullary cavity. 



The fibula (fb.) is a longer though more slender bone. As in 

 Monotremes and most Marsupials the head is large, giving an 

 articulation to the femur and having a portion passing up beyond 

 the head of the tibia to give attachment to some of the leg- 

 muscles. On passing downwards the fibula is directed slightly 

 upwards, and it then curves inwards so as to form a wide inter- 

 osseous space. At its lovver end the bone is dilated considerably, 

 and its articular surface is directed slightly inwards. 



In Udenodon baini the tibia, like the femur, is proportionally 

 a much stronger bone than in U. gracilis, and it is also propor- 

 tionally shorter. The head is very large, and from it there runs 

 down the front of the bone a very prominent crest. The fibula, 

 as if to compensate for the greater strength of the tibia, is propor- 

 tionally more slender than in the small species. It gives an 

 articulation to the femur, but the head is much smaller and is 

 scarcely extended beyond the level of the head of the tibia. It is 



Pboc, Zool. Soc— 1901, Vol. II. No. XII. 12 



