94 SHOULDER GIRDLE OF CYNOGNATHUS CHAP. 
pared to that “of Thylacinus or Dissacus.” No one can ex- 
amine the actual sketches of the skull of that Theriodont 
without endorsing that opinion. As a curious detailed point 
of likeness to certain Mammalia may be mentioned “a small 
descending process of the malar bone, which may be a diminu- 
tive representative of the descending element of the malar 
seen in Hotherium, Nototherium, Duprotodon, Macropus, certain 
Edentata, such as Glyptodon, Megatherium, Mylodon, Bradypus, 
but unparalleled so far as Iam aware in fossil reptiles.” (Osborn.) 
The zoologist cannot help being impressed with the significance 
of small details of similarity, which do not seem to be due in any 
way to surrounding conditions of life, and thus referable to mere 
convergence, like the fish-like form of Whales and Seals. 
The rest of the skeleton of the Theriodontia is by no means 
so well known as the skull and teeth. But from what is known, 
other mammalian characters can be pointed out. Perhaps the 
most striking mammalhan feature is to be found in the scapula 
of Cynognathus. It is in this creature somewhat narrow and 
elongated ; but it has a well-marked spine, ending in a hooked 
acromion. Now it. is to be noted in support, so far, of the 
diphyletic origin of mammals, that in the Monotreme, as in 
Whales indeed, the spine forms the anterior border of the scapula, 
and 1s coincident with it, there being thus no prescapula at 
all in the Monotreme, and only a trace of it in certain Whales. 
Whether the multituberculate Zritylodon or Diademodon had 
a scapula after the Monotreme pattern is not known; but it is 
clear that the scapula of the triconodont Cynognathus is quite after 
the pattern of the Eutherian scapula. Furthermore, Professor 
Seeley is of opinion that the coracoid was relatively small, and 
indeed smaller than the same bone in Edentates, and a fortiori 
than in Monotremes. Another fact of structure which points 
also, possibly, in the direction of a diphyletic origin for the 
Mammalia, is the double-headed ribs of Cynognathus. As is well 
known, the ribs of the Monotremata have only the central head, 
the capitulum. 
As a general mark of affinity with mammals the reduction of 
the intercentra in Cynognathus may be noted, and also the 
existence of a small though perfectly obvious obturator-foramen, 
separating the pubis from the ischium. There are further details 
' It may be necessary to exclude the Whales from the comparison. 
