84 
PROFESSORS T. W. BRIDGE AND A. C. H ADDON 
ment to the outer surface of the spatulate process of the scaphium internally and its 
insertion into the anterior extremity of the tripus externally. The insertion of the 
discoidal extremity of the horizontal process of the intercalarium into the middle of 
the ligament completely divides the latter into two portions, the fibres from the 
scaphium being inserted into the inner face of the disc, while those passing to the 
tripus have their origin from its external face. 
The tripus (figs. 12 to 14, tr.) difters considerably in shape from both the scaphium 
and intercalarium, and is a much larger ossicle than either. In shape it is a thin 
flattened bone with its surfaces looking respectively upwards and downwards and its 
margins inwards and outwards. The whole extent of the outer margin is convex, but 
much more so posteriorly than anteriorly ; its inner margin, on the other hand, pre- 
sents two concavities, a very slight anterior one, but a much deeper one posteriorly. 
As the tripus passes forwards from its posterior insertion into the dorsal wall of the 
air-bladder to its ligamentous connection with the intercalarium and scaphium in front 
it lies along the lateral surfaces of the complex centrum and the body of the first 
vertebra, and for the hinder two-thirds of its extent is in close relation by its dorsal 
surface with the under side of the broad flat root of the transverse process of the fourth 
vertebra (figs. 3 and 4, ti'.a., tr.c.). The ossicle is divided into three well-marked and 
extremely characteristic })rocesses which have much the same general relations to one 
another that the ramus, the condyle, and the angular process have in the Mammalian 
lower jaw. For reasons which will be sufficiently obvious we may designate them the 
anterior, articular, and crescentic processes. The anterior process (figs. 12 to 14, tr.a.) 
lies along, and parallel to, but by no means in contact with, the lateral surfaces of the 
body of the first vertebra and the anterior third of the complex centrum, or, more 
strictly speaking, in a line with the junction of the dorsal and lateral surfaces of those 
centra, but its anterior extremity projects so far in front of the centrum of the 
first vertebra as to be exactly opposite the external atrial aperture, and the convex 
outer surface of the spatulate process of the scaphium (figs. 4, 9, 21, and 22). The 
anterior process is a thin, flattened, lamina of bone, slightly convex along the outer 
margin, and as faintly concave on its inner border. The somewhat greater length 
of its outer as compared with the inner margin, gives to the truncated anterior 
extremity of the process a slightly thickened and nearly straight edge, which looks 
directly inwards towards the spatulate process of the scaphium, and it is to this 
thickened edge that the outer extremity of the interossicular ligament is attached. 
The crescentic process is a direct continuation backwards of the anterior process, and, 
like the latter, is thin and flattened, although much more slender. Nomially, the 
whole of the process, with the exception, perhaps, of a small portion of its root, is 
imbedded in the tunica externa of the corresponding half of the dorsal wall of the 
anterior compartment of the air-bladder (figs. 18 and 19, D\c.). The root of the 
crescentic })rocess is In a line with the anterior process, but for the posterior two- 
thirds of its extent the process becomes more slender, and at the same time, rather 
