42G 
MR, W. K. PARKER OK THE SKELETON 
“Amniota” than in the “ Anamniota;” especially, as I have noticed, in the Turtle and 
Crocodile ; its outline, as distinct from that of the paired trabeculee, can be traced in 
embryo Mammals, especially Marsupials. Here, its presence, even for a few days, as a 
distinct element, is very instructive, showing that, in some respects, the Petromyzoids 
lie between the Myxinoids and the Anura. In some respects; —but the larval Anura 
(see “ Batrachian Skull,” Part III., Plate 30, figs. 10, 11, p.e.) show very clearly the 
independence of tbe “ anterior intertrabecula,” which has no existence in Petromyzon, 
but is so remarkable in the Myxinoids (same Plate, figs. 2, 3, a.i.tr.). In those forms 
it supports the prenasal proboscis; in the larval Anura, with symmetrical nasal 
capsules, it forms the wall of partition between them, whilst the short narial passages 
acquire, each, a crescentic valvular cartilage, representative of the series of imperfect 
rings in the Myxinoids. 4 ' 
In spite of the difference of form and of the character of its tissue ( hard instead of 
soft cartilage), and of its very temporary separateness, no one can fail to see its mor¬ 
phological identity with that of the Myxinoids (Plate 10, figs. 2, 3, and figs. 4, 5, p.i.trf-f 
This small, scarcely transformed skull of the Lamprey shows exactly what has been 
built upon the Ammoccetine foundations (see Plate 19, figs. 4, 5 ; and Plate 10, figs. 
4, 5). Outside the newly floored fore part of the skull, a flange or wing of cartilage 
has been added, which widens from behind forwards, until it shoots out right and left, 
as the ethmo-palatine ( e.pa .) This flange runs round the looped trabeculae in front, 
and thus the ethmo-palatines have an elegant, narrow, arched commissure running 
concentrically round the front of the early trabecular commissure. 
This peculiar structure explains what was to me very anomalous in the transforming 
skull of the huge Tadpole of Pseudis (“Batrachian Skull,” Part III., Plates 11, 12) 
where these bands are seen to pass into each other, under the ethmoidal region of the 
skull, and to have a distinct margin, marking the commissure off from the basis 
cranii, behind the transverse band. Here, however, there has been coalescence of the 
basi-cranial flange with the ethmo-'palatines, for in the Ammoccete (Plate 12, figs. 4, 5), 
the subocular band of cartilage is only developed in its hinder third ; in the Tadpole 
these parts are primarily continuous. 
The secondary character of the cornu trabeculae ( c.tr .), is shown in this little skull, 
* In retaining the old human-anatomy names, for descriptive purposes, in special districts or regions, 
the morphologist is saddled with a double nomenclature. For as our conception of the development of 
the parts becomes more and more clear, there must of necessity arise a number of general terms, each of 
which may include several special descriptive terms. Thus, the general morphological term “ intertra¬ 
becula,” which I have added to Rathke’s term “trabeculae,” includes the perpendicular ethmoid, and 
the septum nasi ; the prenasal rostrum ; and the median part of the anterior and posterior sphenoidal 
regions. 
f It is due to the late Professor F. M. Balfour to state that the determination of the cranial nature of 
this peculiar median cartilage of the Myxinoid skull is due to him, and that this was seen independently 
of the peculiarly conclusive instance of it in the young Lamprey. It seemed to me, for a while, to be a 
median palatine cartilage, forming a floor to the “ posterior nasal canal,” and putting this view forward 
to him, as a suggestion, his immediate answer was, “ No ; it is your intertrabecula.” 
