546 
ME. W. K. PAEKEE ON THE STEUCTUEE AND DEVELOPMENT 
I do not, then, find these two pairs of basicranial cartilages distinct now for the first 
time. What is new and suggestive is the immense size of the parachordal region of 
the trabeculae, and its earlier birth than that of the hinder plates. Some cause or 
causes, unknown, have given rise to the anachronism of the vertebrae directly behind the 
occiput and the trabeculae on the one hand, and the great occipital ring on the other. 
The common sphenoidal wall is chondrified fully a fortnight (perhaps three weeks, 
even) before the lateral occipital wall. I strongly suspect that the auditory capsules 
oppress the growth of the occipital ring (or segment), making it to be later in its growth 
than other parts*. 
Whilst the hind brain has only the protection of the implanted ear-capsules, the 
mid brain has a high wall, the common sphenoidal crest of the trabeculae ; this part is 
somewhat incurved, but does not form a “ tegmen cranii.” 
The fore brain has merely membranous walls, but it has a cartilaginous floor in 
front ; for the round trabecular rods have become longer and twice as near together in 
front, and besides this they are conjugated in front by a transverse plate of new 
cartilage. 
This plate has three regions ; the middle is the “ internasal plate ” ( i.n.c ), and the outer 
pair are the trabecular cornua ( c.tr .). 
These appear first, and lacking a stage, in the Axolotl ; to show this I refer to my last 
Plate (Plate 29. figs.l, 2), which, happily, shows separate trabeculae, running to the frontal 
wall, each giving out a pedate “ cornu : ” the internasal plate is not yet developed. 
These three regions (Plate 22. figs. 4, 5, i.n.c., c.tr.) have equal, rounded, front 
margins; the cornua make a falcate curve; and on their outer edge the nasal sacs ( ol .) 
partly rest ; the internal nostril ( i.n .) is seen in this concavity. The primordial pitui- 
tary region is now a large oval fontanelle, elegantly regular in form ; and this egg-shaped 
space is about equal in area to the narrower but longer space behind, which is floored on 
the right and left by cartilage. The roofs of the nasal sacs (ol.) are membranous as 
yet ; of the chondrification of the sclerotic I take no note, as it does not graft itself on 
the basicranial stems ; but the ear-capsules seem as closely related to the basilar carti- 
lages as carpels to an axis. 
The simple egg-like auditory sac, only partially chondrified in the last stage, has now 
a complete shell of hyaline cartilage, which has grown big with various swellings that 
are modelled on the membranous labyrinth, whose three “ canals ” are now well seen, 
both in opaque and in transparent preparations of the skull (Plate 22. fig. 4, a.s.c., h.s.c., 
p.s.c.). 
Below (fig. 5), the vestibule, with its contained otoliths ( ot .), swells the general surface ; 
and here the cartilage which was perfectly distributed over the membranous contents 
has undergone dehiscence. 
* The consideration of morphological anachronism is being constantly forced upon me by the study of the 
Amphibia ; this is so great in the common Batrachia, in certain parts, notably the upper parts of the hyoid 
arch, that Professor Huxley himself has not found it easy to harmonize their homologies. 
