164 OSSEOUS, MUSCULAR, AND NEllVOUS SYSTEMS 
tion of the scapula which, from a veiy obvious analogy, I 
should call its acromial process. The scapula itself is shaped 
like that of a bird ; and, in addition to its acromial process, 
by which it is connected to the clavicle, sends a very strong 
process backwards and inwards, towards the upper bone of 
the sternum, with which it is articulated : and it is even 
somewhat connected with tlic bone which I have called the 
flat portion of the clavicle. Along the whole inner margin 
of the process of the scapula joining the sternum (and which 
bears so great a resemblance to the true clavicle in birds)^ 
is placed a thin flat semicircular plate of bone, which, run- 
ning up behind the broad clavicular bone, performs exten- 
sive circular motions during the action of the anterior ex- 
tremities, as well by reason of the laxity of its connection, 
with the clavicular bones, as by its loose hinge-like joint 
with the scapula. It is exceedingly difficult to decide on a 
name for this very singular bone, and to trace its analogies 
throuohout the rano^e of vertebral animals. In the mean 
time, until that be satisfactorily done, it must be evident, I 
think, to all, that its analogies ought to be sought for in 
the class of Reptiles : for, in most species of this class, 
there would seem to prevail an analogous structure, though 
occasionally very complex, and with difficulty to be made 
out. The extreme laxity of the articulation of the scapula^ 
in the Ornithorynchus, and its anomalous bone or process, 
in the other. There are several other differences sufficiently remarkable. 
The peculiar flat semicircular bone forms a great portion of the glenoidal 
cavity in the fossil animal, and the scapula does not seem to be in any 
way articulated with the sternum, unless we consider the bone marked b 
(see the drawing) as the anterior bone of the sternum. Neither of these cir- 
cumstances holds with regard to the Ornithorynchus paradoxus. There is a 
considerable resemblance between the shoulder-bones of the fossil animal 
and the common Chameleon, a r-keletnn of ivhich I have placed before the 
Society. 
