224 FISHES CHAP. 
the whole length of its dorsal border the palato-quadrate carti- 
lage is fused with the inferior lateral margin of the cranium from 
the periotic to the olfactory region, thus forming a triangular 
plate of cartilage, the base of which is continuous with the 
cranium, while the downwardly directed apex provides an articu- 
lar surface for the lower jaw. The hyoid arch is little better 
developed than the succeeding branchial arches, and includes a 
vestigial hyomandibular, an epi-hyal, and a cerato-hyal. As in 
other autostylic skulls the hyomandibular element is attached by 
ligament to the hinder margin of the palato-quadrate, instead 
Fic. 130.—Side view of the skull of a Sturgeon, with the investing membrane bones re- 
moved. «@, Pharyngo-branchial ; AF, antorbital or lateral ethmoid cartilage ; 4 R, 
articular; 6, epi-branchial ; c, cerato-branchial ; C, notochord ; Cop, basi-branchials ; 
d, hypo-branchial ; De, dentary ; GA, auditory capsule ; Hm, hyomandibular ; hy, 
cerato-hyal ; Zh, inter-hyal ; Md, lower jaw ; Na, nasal capsule ; Od, neural arches ; 
Orb, Orbit ; PF’, post-orbital process; PQ, palato-quadrate; Ps, Ps’, Ps’, para- 
sphenoid ; Psp, neural spines; Qu, quadrate; R, rostrum; Ri, ribs; Sp.N, 
foramina for spinal nerves; Sy, symplectic ; WS, vertebral column; a, foramen 
for the vagus nerve ; I-V, branchial arches ; II-V, foramina for the optic and the 
fifth cranial nerves. (From Parker and Haswell, after Wiedersheim. ) 
of being directly connected with the periotic capsule, and 
obviously takes no part in supporting the jaws. Branchial 
rays for the support of the operculum are attached to the 
cerato-hyal, and some of them have their bases fused together. 
The five branchial arches resemble those of the Dog-Fish, except 
that they tend to become concentrated beneath the skull. 
The existing Chondrostei,' and especially the Sturgeon, are 
remarkable for the persistence and continuous growth of the chon- 
drocranium, and the absence of true cartilage bones. Numerous 
1 W. K. Parker, Phil. Trans. 173, 1882, p. 1389; Bridge, Phil. Trans. 169, 
1878, p. 683. 
