418 H. B. POLLARD, 



last vertebra which takes part in the formation of the cranium. Fur- 

 ther forwards it lies between the cranium and the parasphenoid divid- 

 ing and passing out with each wing of the latter to join the efferent 

 1st branchial. The common trunk thus formed runs on as the oph- 

 thalmic artery on each side. 



The postcardiac portion of the aorta gives off as mentioned above, 

 the artery to the intestines and then the subclavians on each side, 

 continuing as the dorsal aorta backwards beneath the vertebral column. 



The existence of the precardiac portion was mentioned by 

 Müller and it is of importance for it is exceedingly primitive. It 

 occurs (Ayers) in Chlamydoselachus and several sharks and is one 

 more indication of the genetic connection between them and Polypterus. 

 It is also seen in Myxine. 



The persistence of the 3rd branchial artery is a character often 

 seen in Amphibia. The general homology of the vessels is wellknown. 



On the suspension of the jaws (fig. 20). 



On examining the hyomandibular it will be seen that it can take 

 very little part in the suspension of the jaws a point referred to 

 before. It is however very large in size and its service is to bear 

 the operculum. The operculum is stated by van Wuhe to show car- 

 tilage at the joint so that it does not represent merely a membrane 

 bone. 



The upper jaw is tied by the tough skin of the palate to the 

 parasphenoid for considerable part of its extent but posteriorly it is 

 very free, a fact corresponding with the great development of the 

 Levator maxillae superioris. The outer posterior edge is fastened to 

 the posterior edge of the preoperculum and in fact the opercular series, 

 hyomandibular and upper jaw are raised together by this levator 

 muscle. 



The ethmopalatine ligament is extensive and Selachian in appear- 

 ence. The pterygopalatine bar flattens and curves above the ecto- 

 pterygoid but near the ethmopalatine articulation it is rounder in 

 section. At the articulation it is ossified. In front it is prolonged 

 some little way and this prearticular portion is long unossified. 



Comparing this suspension with that of Chlamydoselachus it will 

 be seen that once more we meet with similarity. The bend in the 

 hyomandibular of Polypterus, though signified in Chlamydoselachus is 

 secondary and developed with the development of the operculum from 

 the opercular fold. Branchiostegal rays are present in Chlamydo- 



