448 MR. ST. GEORGE MIVART ON THE 
The preaxial margin shows two elongated coracoid grooves, which form with each 
other an angle of about 120°. These two grooves nearly meet together in the middle 
line (fig. 77, ec). 
The ventral (inferior) margin of the grooves does not extend so far preaxially as does 
the dorsal (superior) margin, especially towards the outer ends of the grooves. 
At the middle of the dorsal margin there may be a wide notch or a slight median 
prominence. Between this notch or prominence and the outer ends of the dorsal lip of 
the preaxial margin that lip is concave, owing to the production preaxially and outwards 
of the costal angles (fig. 77, ca). 
The postaxial margin of the sternum is deeply excavated, owing to the prominence 
of two external xiphoid processes (fig. 77, Jz). In the middle of the postaxial margin 
there is a prominence, the median xiphoid, which, however, does not extend far 
(fig. 77, mz). Between this and each lateral xiphiod there is another rather irregular 
and less marked prominence. 
Each lateral margin of the sternum is slightly concave, owing to the angle (about 
155°) formed by the external margin of the lateral xiphoid with that of the pleurosteon. 
The pleurosteon has a very wide and excavated external margin to receive the dorso- 
ventrally expanded ends of the sternal ribs: it is divided by five more or less complete 
bony septa, between which are, in the dry skeleton, five deep excavations (fig. 79). The 
edges of these septa proceed obliquely ventrad and postaxiad; and each develops two 
convex articular surfaces (one at the dorsal and one at the ventral part of each septum) 
for the corresponding articular concavities of the sternal ribs. The first septum has 
these articular convexities most prominent and most approximated (fig. 79, 7s). The 
fifth septum has them but very slightly marked. 
‘VERTEBRAL PARTS AND PROCESSES. 
It remains now, in conclusion, to consider the several parts and processes of the 
vertebra, as regards the varying condition of the same parts in different regions of the 
spinal column. 
Centra. 
With the exception of that of the atlas, each centrum is connected by suture or 
anchylosis with the rest of the vertebra to which it belongs. 
In absolute size the centra of the true dorsal vertebre excel. 
Except the preaxial surface of the axis (and apart from the atlas) all the cervical and 
true dorsal vertebree have their centra concayo-conyex at each axial end. 
The centra may, however, be slightly biconcaye, as in some of the caudal vertebre. 
Adjacent centra may be anchylosed together from the twenty-sixth to the forty-sixth 
vertebra inclusive. 
