474 J. W. HITLKE ON THE STEENAL APPAEATTJS IN IGrANODON. 



differences are, I think, fairly attributable to mutilation and com- 

 pression. The symmetry of their junction with the azygos bar 

 strongly favours the belief that we see here preserved the undis- 

 turbed normal relation of the several parts. On this supposition 

 the two divergent rods occupy precisely the position, and they have 

 the same relation to the azygos bar or interclavicle (PI. XIY. 

 fig. 3, id) as the clavicles in extant Lacertilia ; for the apposition of 

 their outer ends to the process termed " acromial " on the anterior 

 border of the scapula will hardly be doubted. 



The azygos piece (PI. XIY. fig. 1, id) has the form of a long 

 flattened bar, the width of which appears to increase slightly from 

 that which I regard as its anterior end to a point about 9*5 cm. 

 behind the clavicles, and thence to decrease slightly to the posterior 

 extremity. The anterior extremity, which advances slightly in front 

 of the mesial ends of the clavicles, is indented at its middle. The 

 posterior margin is nearly straight, but I do not feel certain that 

 this is a natural edge, and that the bar may not originally have 

 been somewhat longer. The lateral borders for the space of 7 cm. 

 behind the clavicles to the point where the bar attains its greatest 

 width are smooth and arcuate, suggestive of having formed a small 

 segment of a long curved articular groove for the reception of an 

 epicoracoid; whilst the remainder of the border behind this is 

 rough, uneven, and apparently non- articular. A mesial ridge or 

 low keel divides the bar longitudinally. Its greatest elevation is 

 about 1*5 cm. 



Measurements of Azygos Bar. 



Length 39*4 cm. 



Width at anterior extremity 11°0 „ 



Maximum width, behind clavicles .... 15-3 „ 

 Length of exposed arcuate part of 



lateral margin about . 7*0 „ 



Width at posterior end of bar 10*0 „ 



What is this azygos bar? That it comprises the interclavicle 

 (ParJcer) ( = epistemum of some authors, the clavicular sternum, 

 Hoffmann\ is, I submit, demonstrated by its connexion with the 

 clavicles, which, as I have already said, agrees with that obtaining 

 in existing Lacertilia. But does it comprise the sternum (costal 

 sternum, Hoffmann) also ? Marks of connexion of costse with 

 its lateral borders would be decisive of this, but none are recog- 

 nizable. The extent, of the arcuate part of the lateral border 

 is quite incommensurate with the size of the arc which we know 

 the mesial border of the epicoracoid must have had. Lastly, the 

 figure of the azygos bar is quite unlike the shield-like sternum of 

 extant Lacertilia and Crocodilia. 



These considerations weigh with me in regarding the azygos bar 

 as an interclavicle only — the homologue of that of now living 

 Lizards, and of the bony sternum, so called, of extant Crocodiles. 

 If this view is correct, the bar was splinted to a shield-like sternum 



