OF THE SKULL IN LEPIDOSTEUS OSSEUS. 
483 
relatively) ; its intrinsic centre also, the articulare, has become two separate points 
of bone (Plate 38, fig. 5, ar.). The rest of this long, subarcuate, terete rod (raJc.), 
runs along the grooved inner face of the dentary (d.) nearly to its distal end. The 
coronoid crest ( cr.c.) is a very large “ear” of cartilage; it is convex outside and 
hollow within ; its fore part is a free lobe. 
The hyomandibular (Plate 37, fig. 4, and Plate 38, fig. 5, hm.) is a remarkable bar, 
about half the size of its “ serial homologue ”—the suspensorium. Its arched, 
extended head is a convexo-concave condyle for articulation under the horizontal 
canal; behind this there is a cartilaginous knob for the opercular bone. The bony 
shaft is short, pinched in the middle, and has an oval fenestra near its front third. 
Below the shaft it swells out into a solid bilobate mass, the lesser lobe being behind. 
In front of the fore lobe, on the inside, there is a concavity for the inter-hyal ( i.hy .). 
The bar from that point becomes the small sigmoid symplectic (sy.) ; it is bent 
downwards suddenly, and then runs straight forwards to lie along the inside of the 
hinder third of the lower edge of the suspensorium. 
Its bony shaft occupies its hinder two-thirds; where it becomes.straight, there it 
has a small bony elbow; its fore end is a blunt point (Plate 38, fig. 5, sy.). 
The inter-hyal {i.hy.) is a small pyriform cartilage, its narrow end fits into the 
concavity in the hyomandibular, and its broad end has a cup on its inner side for the 
head of the cerato-hyal (c.hy.). 
The latter segment has a “ trochanter ” behind its small rounded head; its shoulder 
is ossified as a separate epi-hyal {e.hy.) ; the main shaft {c.liy.) has its own centre; 
it is narrower in the middle, and is only separated from the stylo-hyal by a tract of 
cartilage. 
The rounded lower end of the cerato-hyal fits into the oblique shallow cup of the 
sub-globular hypo-hyal (h.hy.) ; this short segment is ossified on its outer face ; at 
present, at any rate it has no second centre, as in the Teleostei; but in these, as in 
Acipenser, it is completely segmented off from the cerato-hyal. 
The basal piece {h.hy.) is a large “ inter-glossal ” plate as long as all these three 
segments above it; it is oblong, rather pinched in the middle, emarginate in front, 
thickish, and somewhat fibro-cartilaginous, having cross-bands and reticulating, con¬ 
nective fibres, wrought into it on its upper surface, and its hyaline cartilage somewhat 
softer than in the other parts. 
The basal piece of the branchial system, and part of the first part of hypo- 
branchials ( h.hr ., h.hr.) are figured. For the rest, I must refer to the figures and 
descriptions of the last stage; these parts have not altered in any important degree 
—except in size. 
Comparison with other types, and Summary. 
As soon as the primordial cranium becomes sufficiently differentiated—as hyaline 
cartilage—to be distinguished from the rest of the cephalic mesoblast, we find a 
