(B) _Chondrocranium[28]._--In front of the vertebral column lies the cartilaginous trough, the chondrocranium, which protects the brain. This consists of a praechordal portion--developed out of a pair of lateral cartilaginous rods--the _trabeculae cranii_--and a parachordal portion lying on either side of the anterior end of the notochord. This arises in development from a cartilaginous rod (parachordal cartilage) lying on each side of the notochord and possibly representing a fused row of dorsal arcualia. The originally separate parachordals and trabeculae become connected to form a trough-like, primitive cranium, complete or nearly so laterally and ventrally but open dorsally. With the primitive cranium there are also connected cartilaginous capsules developed round the olfactory and auditory organs. There also become fused with the hinder end of the cranium a varying number of originally distinct neural arches. [Illustration: _A._ After W. K. Parker, _Trans. Zool. Soc. London_. _B._ After Gegenbaur, _Untersuchungen zur verg. Anat. der Wirbeltiere_, by permission of Wilhelm Engelmann. _C._ After Hubrecht, Brown's _Tierreich_, by permission of Gustav Fischer. FIG. 15.--Chondrocranium, &c. of _Scyllium_ (A), _Notidanus cinereus_ (B) and _Chimaera_ (C). Br.A, Branchial arches. olf, Olfactory capsule. c.h, Ceratohyal. ot, Auditory capsule. e.p.l, Ethmopalatine ligament. p.pt, Palato-pterygoid bar. Hm, Hyomandibular. p.s.l, Prespiracular ligament. M, Meckel's cartilage. r, Rostrum.] o, Orbit.