192 PROF. W. K. PARKER ON THE MORPHOLOGY 



Prom the front of the ear-capsules to the frontal wall there is nothing hut a pair of 

 cartilages, the trabeculse ; these hulge externally, are concave within, are of moderate 

 height, that is, they are as high as this flat skull is within, reaching ahove to the frontals 

 and parietals [f,p), and helow to the parasphenoid (pa.s). 



As they approach the nasal sacs they become flat and depressed ; having lost their wall 

 character, they became part of thejloor only. Each plate of cartilage is bowed outward 

 twice — first in the alisphenoidal region, and again in the ethmoidal ; but on the whole 

 they gently approximate, but are a good distance apart at their end. Then they are 

 first rounded and then each is Battened out into a small flabelliform " cornu " (c.tr). 



Close behind these cornua the trabecule are undergoing conjugation, each bar 

 sending inwards a small internasal lamina (i.n.c). Between the body of the premaxillary 

 and these processes there is a large internasal cavity (m.n.p). 



In similar larva? of Salamandra maculosa (PI. XIV.) the notochordal region was well 

 floored with cartilage, the large expanded ends of the trabecular having coalesced with 

 equally large parachordal tracts. Even in the adult of that kind there was still the 

 trabecular bridge, then a fontanelle, and then the true parachordal tract. Here, however, 

 so early in life, the parachordal cortilages only form a conjugating belt over the end of 

 the parasphenoid (pa.s). Thus it is evident that all the inturned parachordal part of 

 the trabecular and of the fore half of the hinder cartilages, or true parachordals, have 

 been entirely absorbed, leaving the vicarious parasphenoid to make the floor. 



I have watched this process in larva? of Triton cinstatus and mJS T otophlhalmus (Pl.XVIL). 

 In this latter kind two larvae of precisely the same size differed greatly ; in one (figs. I & 2) 

 the trabecular ends were reduced to a small lobe, and in the other (fig. 3) they were still 

 of good size, but they had become quite free from the hinder cartilage. 



In both Proteus and Menohranchus the adult skull is much simpler than the embryonic. 

 My dissection of the latter kind shows more basal cartilage than the one dissected by 

 Professor Huxley (loc. cit.). In small young specimens I am confidently expecting to 

 find a much fuller development of the basal cartilage than is to be seen in the adult *. 



At present, as in the adult Proteus, there is, as yet, no olfactory cartilage ; the sacs 

 lie on and outside the trabecular. Behind the internal nostrils (i.u) there is on each 

 side a free cartilage having a totally different morphological meaning to the nasal 

 sacs, namely the ethmopalatine (e.pa) ; it is a small semioval free bud, attached to the 

 trabecula at its postnasal bend, and is the orbito-nasal landmark. 



The postorbital region is marked off by the large suspensorium, whose condition 

 suggests considerable ripeness in this embryo, much in contrast with the slow meta- 

 morphosis of the fore part of the head. 



The condyle is opposite the optic foramen ; the cartilage next to it is ossified as a 

 quadrate (q), but from the middle all is soft. The true swinging-point is bilobate, 



* I am not aware that any brain-bearing vertebrate shows a more simple cranium in its early condition than the 

 larvae of the Urodeles ; but they possess every thing that is wanted to make up a " ehondocranium " in any type. 

 Birds and mammals have nothing but the two " parachordal " cartilages, passing into the two " trabecular cranii," 

 and the two " intertrabecular " tracts ; and even these are, I suspect, merely differentiated, the parachordals from 

 the trabecular, by the latter getting the start in chondrification. 



