DEVELOPBCENT OF THE SKULL EST THE UEODELES. 211 



as that of the Newt, we shall find that only those scutes have been retained in the latter 

 that are always the most constant in the Vertebrata above the Ichthyopsida, altogether. 



This fact is disclosed at once when we see that most of the surface-plates in the 

 Newt's skull can, in a moment, be named by the same names that their representatives 

 have received in the highest Birds and in the highest Mammals. 



These are they that were at first brought, in the Ganoid Fishes, under the influence 

 of the brain in its regions, of the sense-capsules right and left of the brain, and 

 of the apparatus and armature of the mouth. 



We see, also, that the Newt has dropped (suppressed), even in its larval state, 

 the special scutes that protect and amplify the branchial apparatus in the Ganoid 

 and Osseous Fishes ; these are here sujjpressed at once and for ever (with the slight 

 exception of a few parts that are retained for new functions) in every ascending branch 

 of the Great Vertebrate Life-tree. 



A list of the superficial bones to be found in the Newt's skull will seem to be rather 

 that of some growing Bird or Mammal. They are as follows : — 



1, frontals ; 2, parietals ; 3, nasals ; 4, squamosals ; 5, premaxillary ; 6, septo- 

 maxillaries (found in certain Birds); 7, maxillaries ; 8, vomers; 9, palatines; 10, 

 pterygoids; 11, parasphenoids (existing in three pieces, early united, in the Bird, and 

 as two (hinder) ossicles — the " cornua sphenoidalia " in certain Mammals) ; 12, 

 dentaries (or mandibular rami) ; 13, splenials (constant in the Bird class). 



In the endocranium the low, and perhaps archaic-selachian, origin of these forms 

 is indicated by the generalized nature of the truly bony tracts. In the Selachians we 

 only see the crowding of the superficial calcifications of the cartilaginous structure in 

 certain parts; here, in the Newt, calcification rapidly passes into ossification, but the 

 " centres" run riot over two or three morphological territories at once, and do not keep 

 to proper interneural spaces. 



Yet, even thus, the nomenclature is not dilficult'; the terms merely have to be com- 

 pound, like the parts they stand for ; the " sphenethmoid " is, for example, a bone 

 answering to the sphenoid and ethmoid of human anatomy. 



I have compared Triton with Lepidosteus for the sake of illustration, and not as 

 seeking to derive the Newt from that or any such Ganoid Fish ; 1 am not speaking of 

 actual genesis, but of the general order of the specialization of parts. 



On the other hand, I am inclined to think that the Urodeles came up from types 

 that specialized their dermal scutes very sparingly, like the Lijjidosiren ; whose ancestors 

 (probably) had simple chondrocrania that had subjected the dermal armature to no 

 special modification. 



Within the limits of this small contribution I have been able to show how remark- 

 ably the stages of a small high " Caducibranch " correspond with the permanent 

 condition of large and low types. 



But if to this paper we add Dr. Wiedersheim's invaluable memoirs, and the other 

 VOL. XI, — PAKT VI. No. 6. — January, 1882. 2 k 



