. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. SKELETON. 151 As will be recalled, the notochord extends forward as far as the infundibulum, and its anterior end is concerned in the formation of the chondrocranium. On either side of this struc- ture there develops a horizontal cartilaginous plate, the para- chordal cartilage, which grows out laterally until it unites with a cartilaginous box, the otic capsule, which forms around the sac-like inner ear (p. 71). From this union of parachordals and otic capsules, there is formed a trough which encloses the me- dulla oblongat
. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. SKELETON. 151 As will be recalled, the notochord extends forward as far as the infundibulum, and its anterior end is concerned in the formation of the chondrocranium. On either side of this struc- ture there develops a horizontal cartilaginous plate, the para- chordal cartilage, which grows out laterally until it unites with a cartilaginous box, the otic capsule, which forms around the sac-like inner ear (p. 71). From this union of parachordals and otic capsules, there is formed a trough which encloses the me- dulla oblongata below and on either side. Later, in the typical conditions, the cartilage gradually extends upwards and inwards. Fig. 159. Early chondrocranium of Amblystoma, before the formation of the otic capsules, ap, ascending process of quadrate; bq, body of quadrate; dp, descending process of quadrate; ?«, Meckel's cartilage; «, notochord; oc, of, foramina for oculomotor and optic nerves; p, parachordals; /, trabecula; trc, tra- becular crest. From Winslow. from the dorsal surface of the otic capsules forming a plate — the synotic tectum — which roofs in this region of the brain above. To this region there is added (amphibia) a vertebra or vertebral complex, developed like those of the vertebral col- umn, which becomes finally united to the parachordals and otic capsules, and closes in the cranium behind. Comparative mor- phology would also lead us to regard the parachordals as formed of coalesced vertebral centra ; but in their history, so far as made out, they of themselves afford not the slightest clew as to the number of elements fused together in this region. The trabeculae cranii are a pair of cartilaginous rods which. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Kingsley, J. S. (John Sterling), 1854
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