On the Anatomy and Phylogenetic Position of Polypterus. 419 



selachus and it is probably their inclusion in the operculum of Poly- 

 pterus that gives the cartilaginous articulation. 



The prearticular prolongation of the pterygopalatine cartilage of 

 Polypterus is of importance and points to a former extension as in 

 Chlamydoselachus. 



Passing to the Urodeles we find that the quadrate has become 

 the sole suspensorial element and further that it shows many variations. 

 The condition in Menopoma appears to me to be the most typical 

 and primitive. Here only the anterointernal process is fused with 

 the cartilage. The pterygoid cartilage is a separate piece, the dermal 

 bones having taken away all the function of the pterygopalatine bar. 



Prof. WiEDERSHEiM has pointed out to me that Menopoma Hes 

 in the direct line of general Urodele descent. The state in the rest 

 of the Urodeles, that is to say the prolongation of the posterointernal 

 angle to the auditory region is not specially difficult to derive from 

 the typical condition. 



In Ranodon the pterygopalatine bar fuses with the antorbital 

 process remaining continuous. It extends at some distance from the 

 base of the skull. So here the tendency of the palatine to fuse with 

 the antorbital process with loss of the articulation is manifested in 

 the Urodeles. It is seen in the developing Lepidosteus and also in 

 the tadpole and also in the Cyclostomi. 



Such seems to me the manner of evolution of the Suspensorium 

 of the Amphibia. I do not consider it as derived from that of Chimaera 

 and the Dipnoi by fenestration and reduction of continuous cartilage. 



Thymus and Thyroid (fig. 21 and 6). 



The thymus is a paired organ lying dorsally to the gill clefts 

 behind the wing of the parasphenoid. It is whitish and slightly lobed. 

 It did not appear to be divided into a number of portions. 



The thyroid is a paired oval body similar in appearance 

 to the thymus lying at the side of the basibranchial between the 

 aortic trunks to the 1st and 2nd branchial arches. 



The oral cavity is curiously prolonged at the side of the tongue 

 into a pouch only separated from the exterior by the skin supporting 

 the jugular plates. Below the tubelike prolongation there lies at 

 the side of the ceratohyoid a yellow glandular mass. 



Similar patches are seen ventrally to the gills (fig. 6). 



