20G PEOF. W. K. PARKER ON THE MORPHOLOGY 



Summary and Conclusion. 



These instances of the Structure and Development of the Skull in the Caducibranchiate 

 division of the Urodeles are intended to be a continuation of my recently published 

 account of the skull in the Tailed Amphibians in the Philosophical Transactions. But 

 I am only in the midst of things at present ; and this paper must be followed by one 

 giving the development of the skull in Triton, the structure of the adult skull in 

 the Menopome and Siren and Amphiume and the skull of an old Sieboldia. 



When time has permitted all these things to appear, and when my fast-growing materials 

 relative to the Anurous type of skull have seen the light (Phil. Trans, pt. 1, 1881), then it 

 will not be difficult to dilate upon the growth and architecture of the skull in these most 

 instructive metamorphosing " Ichthyopsida." Meantime a narrower scope will be of 

 some use ; for the tail-bearing forms undergo great and important changes during their 

 life-history, and in them we seem to see low and ancient types of " Dipnoi " making trial 

 of land-life, and becoming, in very various degrees, adapted to their new surroundings. 



On the other hand, the Batrachia appear to be the terrestrial outcome of low and 

 generalized tribes, which were not Marsipobranchs, nor Chimaeroids, nor Selachians proper, 

 but all these in potency if not in specialization. The few bony plates that in the 

 Dipnoi become attracted to the chondrocranium, and wedded to it — these appear early in 

 the life of each individual Urodele. 



These, and scarcely any others, are the heritage of the lowest Perennibranchiate forms, 

 as Proteus and llenobranchus ; and every larval Urodele is like the fishes at first, and 

 only after a time gains the additional parts that characterize the most developed types 

 of the group. 



Some of these almost rival the more ambitious tailless Amphibia ; they form a sort of 

 parallel " leader " in the vertebrate life-tree, but more simple and more stunted. 



Metamorphoses so wonderful as these Amphibia are seen to undergo (they transform 

 themselves openly, and not in secret places, as is the wont of most Vertebrates), render 

 them invaluable to the student ; for they train the mind, and make it much more easily 

 take the stamp of morphological teachings. 



The Urodeles are inferior to the Batrachia in that they do not often metamorphose 

 their hyomandibular into a columella. This cartilage, or " pharyngo-hyal rod," never 

 gains an annulus tympanicus ; for their first cleft is not only closed, it was never 

 open, and was arrested early. 



One type has a simple hyomandibular, viz. Proteus ; but it remains unchanged, as in 

 Ceratodus, Notidanus &c. 



This type of skull differs from that of the Batrachia in that it never acquires a carti- 

 laginous floor, and its sides, ossifying, do not unite to form a girdle-bone. 



The pterygopalatine arch, such as we see in the Batrachia, is always formed in the 

 Urodeles of two totally separate elements, which never unite ; as in the Skate, there is a 

 distinct " ethmo-palatine " and a pterygoid process of the suspensorium. Moreover, the 

 bony plates that are applied to these two elements begin irrelatively to them, as the 

 homologue of the archaic pterygo-palatine submucous plate of the Dipnoi, by subdivision 



