On the Anatomy and Phylogenetic Position of Polypterus. 41 



On examining the glenoid region it is seen especially in sections 

 that the cartilage which persists between the scapular and coracoid ossi- 

 fications is rodlike (fig. 22). Supposing a Polypterine form to change its 

 habitat from water to land, the pressure on the articulation would be 

 changed and increased and those animals which could develop ossi- 

 fication would have the advantage over those that could not. As can 

 be well seen in the case of the ectethmoid of Polypterus or the 

 pterotic of Teleostei a bone arising thus would become a separate 

 bone and the steps from this condition to that of a perfect humerus 

 are easy to conceive and at the same time also the shape of the 

 articulation can be explained. The articulation between shoulder 

 girdle and fin is a convexo-concave one as between humerus and 

 radius or ulna while the articulation between shoulder girdle and 

 humerus is concavo-convex. This last point appears to me not unim- 

 portant. 



Secondarily in higher animals the independent development of 

 the humerus would be pushed back to the cartilage stage in onto- 

 geny like for instance the palatine cartilage where it occurs. 



It is also conceivable that the humerus should separate off as a 

 block of cartilage but the above view seems more rational. 



On the aortic yessels (fig. 19). 



In commencing this work it was not my intention to deal with 

 the bloodvessels and my observations are by no means complete. Yet 

 certain relations are of great interest. The origin of the aortic trunks is 

 depicted by Müller and Boas. The first branchial efferent artery 

 runs in a groove in the first suprapharyngobranchial and, on leaving 

 it, forward to the orbital wings of the parasphenoid into which it 

 penetrates joining a vessel to be described. A fine nerve can be 

 seen in this region accompanying the artery and joining the Palatine. 

 It may be sympathetic. 



The second branchial artery is very stout. It is the systemic 

 and supplies the dorsal aorta. 



The artery of the 3rd branchial arch of the left side has a similar 

 course to the second but is much slighter. The 4th was not observ- 

 ed to join the aorta at all. The 3rd branchial of the right side 

 showed a difference from that of the left in that it ran into the mesen- 

 teric artery which arises where to two systemics meet. The dorsal 

 aorta runs both forwards and backwards. The precardiac portion 

 penetrates immediately into the skull passing into the body of the 



