616 
ME. W. K. PAEKEE ON THE STETJCTUEE AND 
has assumed a series of curious bendings (Plate 55. figs. 1 & 2) ; the second, or mandibular, 
has developed a free bud at its distal end, and has united itself, by its proximal end, and 
also beyond its middle, to the first bar. The first of these two pairs of conjugations 
show the first condition of the union of the pedicle of the mandible (pd.) with the 
elbowed part of the trabecula ( tr .) near its apex, and the second the rudimentary pterygo- 
palatine arcade (ppg.). The bud of cartilage at the free end of the second bar is the 
free mandible (articulo-Meckelian rod), and all the rest is its suspensorium. The upper 
part of the hyoid arch has not become chondrified ; the lower part, or cerato-hyal 
(fig. 2, c.hy.), has become very much flattened out, and, pressing its antero-superior angle 
against the superior margin of the arch in front of it, has begun to form a remarkable 
temporary articulation, with a joint cavity. Besides the visceral arches, the ear-sacs are 
now enclosed in a cartilaginous capsule ( au .), which is unfinished at the upper part. 
Save the branchial arches and the parts just mentioned, there is no other cartilage in 
the cranio-facial basketwork at this stage, for the “ parachordal ” region (nc.) is still 
membranous. 
The first pair of bars, or trabeculae, extend from their posterior end , which 
overlaps the fore end of the notochord, to the frontal wall of the face, their anterior 
ends running up to the cartilages that form the thickness of the upper lip ( u.l ., here 
shown in outline). On the whole, the figure made by the trabeculae is lyriform, but 
the bars are bowed and bent in the manner of gnarled branches. The apical or 
hinder part is bent suddenly inwards, at little more than a right angle, and this part 
is terete, with a round and somewhat knobbed end. Then the bar thickens, and, being 
bent on itself at nearly a right angle, it runs convergingly inwards. This is done 
twice, the second time in a crescentic manner, suddenly ; and thus the right and left 
bars are brought fairly into contact, their free ends flattening somewhat and then 
becoming clubbed (like the apices), these swollen, distal ends looking outwards, away 
from each other. Thus, with the round end of the notochord stopping the gap behind, 
we have a pituitary space of huge relative extent ; it is heart-shaped, Avith an anterior 
acuminated apex and somewhat concave sides. 
There are the rudiments of two “ myotomes ” {mt 1 , mt 2 ) on the sides of the huge noto- 
chordal extremity, which is somewhat pinched at its waist ; but there is no parachordal 
cartilage. The soft tissue which lies on the muscular segments rapidly chondrifies after 
this time ; so rapidly that in a few days there is no distinction of trabecular and para- 
chordal cartilage (fig. 3, tr., iv.). Thus the trabeculae show their independence by their 
priority ; they are perfect for several days before the investing mass (parachordal region) 
is chondrified. 
In this model and platform of a skull the ear-balls are as independent as the eye- 
balls. At present all the cartilage that exists is below. The cranium, save at the 
base, is a “ membrano-cranium,” and the nasal qouches are soft membrane. 
The posterior or outbent elbow has the pedicle of the mandible conjugated to it; 
the anterior inbent elbow touches that of its fellow of the other side, and these 
