448 ME. ST. ftEOEaE MIVAET 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, c c). 



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, Ix). In the middle of the postaxial margin 

 there is a prominence, the median xiphoid, which, however, does not extend far 

 (fig. 77, mx). Between this and each lateral xiphiod there is another rather ii-regular 

 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 di-y 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 coiTesponding articular concavities of the sternal ribs. The fii'st septum has 

 these articular convexities most prominent and most approximated (fig. 79, is). The 

 fifth septum has them but very slightly marked. 



Veetebeal Paets and Peocesses. 

 It remains now, in conclusion, to consider the several parts and processes of the 

 vertebrae, 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 vertebrce excel. 



Except the preaxial surface of the axis (and apart from the atlas) all the cervical and 

 true dorsal vertebrae have their centra concavo-convex at each axial end. 



The centra may, however, be slightly biconcave, as in some of the caudal vertebrae. 



Adjacent centra may be anchylosed together from the twenty-sixth to the forty-sixth 

 vertebra inclusive. 



