| OCR Text |
Show 42 PROF. T. H. HUXLEY ON CERATODUS FORSTERI. [Jan. 4, quadrate apparatus such as that exhibited by Cestracion. The huge palato-quadrate cartilage (Pl, Qu) of Cestracion is united with the skull in the praeorbital region by a joint, and in the orbital region by fibrous tissue, and answers to that part of the palato-quadrate cartilage of Chimeera which lies between the nasal capsule and the mandible. Fig. 8. Kck Cestracion philippi. Left lateral view of the skull. a, occiput; b, postorbital process; c, c', antorbital process ; d, anterior end of the chondrocranium ; ol, olfactory capsule; Ot.p, otic process, or spiracular cartilage; Sp, place of the spiracle; H.M, hyomandibular cartilage; Qu, articulation of the palato-quadrate cartilage (Pl, Qu) with the lower jaw (Mck); p, part of the palato-quadrate arch which answers to the pedicle of the suspensorium in Amphibia; Hy, hyoid; II, foramen for the optic, and V, for the trigeminal nerves ; 1, 2, 3, 4, the upper and lower labial cartilages; 5, a small cartilaginous style attached by ligament to the mandibular cartilage. The small cartilaginous plate (Ot.p), which is connected only by ligament with the periotic cartilage above and with the quadrate below, answers to the otic process of the Frog's suspensorium. This cartilage lies in the front wall of the spiracle, which in Cestracion is situated low at the sides of the head, nearly in a line with the branchial clefts, or in the position which it occupies in foetal Selachians. Moreover this so-called spiracular cartilage bears a rudimentary gill and is so far comparable to any of the branchial arches*. In possessing this permanent mandibulo-hyoid cleft, or spiracle, which is the homologue of the tympanic cavity and Eustachian tube of the higher Vertebrata, and in the permanence of its rudimentary * Gegenbaur considers the spiracular cartilage to be a ray of the mandibular arch. |
