126 
THE ORIGIN OF VERTEBRATES 
that the primitive cartilaginous skeleton of the vertebrate consisted 
of the following structures (Fig. 53, B), viz. the branchial bars 
iy 
= 
Fic. 583.—COMPARISON OF CARTILAGINOUS 
SKELETON OF LIMULUS AND AMMOCQETES. 
A, Diagram of cartilaginons skeleton of 
Limulus. Soft cartilage, entapophysial liga- 
ments, deep black; branchial bars simply 
hatched; hard cartilage, lateral trabecule 
of entosternite, netted; Ph., position of 
pharynx. 
B, Diagram of cartilaginous skeleton of 
Ammoceetes. Soft cartilage, sub-chordal 
cartilaginous bands, deep black; branchial 
basket - work (first formed part), simply 
hatched; hard cartilage, cranio-facial skele- 
ton, trabecule, parachordals and auditory 
capsules, netted; Inf., position of tube of 
infundibulum (old esophagus). 
forming a basket-work, the 
trabeculee and _ parachordals, 
the auditory and nasal cap- 
sules—a clear proof that the 
cranial skeleton is older than 
the spinal. Of these struc- 
tures the branchial bars are 
the only evidently segmented 
parts. 
Tue Sort CARTILAGE OF THE 
BRANCHIAL SKELETON OF 
AMMOCCETES. 
The study of Ammoccetes 
gives yet another clue to the 
nature of the earliest skeleton, 
for these two marked groups 
of cartilage—the branchial and 
basi-cranial—are characterized 
by a difference in structure as 
well as a difference in topo- 
graphical position. J. Muller 
was the first to point out that 
these two sets of cartilages 
differ in appearance and con- 
stitution, and he gave to them 
the name of yellow and grey 
cartilage. Parker has described 
them fully under the terms 
soft and hard cartilage, terms 
which Schaffer has also used, 
and I shall also make use of 
them here. The whole of the 
branchial cartilaginous skele- 
ton is composed of soft cartilage, while the basi-cranial skeleton, con- 
sisting of trabecule, parachordals, and auditory capsule, is composed 
