Title: Chordate morphology
Identifier: chordatemorpholo00joll (find matches)
Year: 1962 (1960s)
Authors: Jollie, Malcolm
Subjects: Morphology (Animals); Chordata
Publisher: New York, Reinhold
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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rupted above by openings for the eyes and by the pineal nasal organs. The nasal opening lay just anterior to the eyes; it was partly divided into anterior and posterior openings in the cephalaspids (Figure 5-31). Behind the eye openings was a depression, closed above by a mosaic of small plates; this was the dorsal field. To either side were similar anterior and posterior lateral fields. Posteriorly the trunk part of the shield had a dorsal crest. Laterally the shield had small folds. Ventrally, the mouth and pharyngeal area was open. The lateral and posterior margins of this ventral opening had ten notches, decreasing in size from in front backward, for the outer branchial openings. This area was covered in life by a mosaic of small plates, except for the mouth and branchial openings. The T-shaped mouth was in the ante- rior part. The endocranium and visceral skeleton of the tremataspid is not well known but was probably like that of the more advanced cephalaspids, which have been described in detail (Figure 5-31). The endocranium and visceral skeleton were indistinguishably fused with each other and with the dermal carapace. They were in part identifiable as only perichon- drally ossified. The degree of ossification varies from .solid to superficial. The cranial cavity opened anteriorly into the nasal cavity, which opened to the outside. The inner ear was enclosed in a bony capsule, and, from the vestibular cavity, a number of canals radiate to the dorsal and lateral sensory fields. The walls of the cranial cavity were pene- trated by many nerve and vascular foramina. The seventh nerve passed through the vestibular cavity. The bone of the endocranial margin was penetrated in the later forms, but not the tremataspids, by large venous sinuses. The notochord was much constricted, lying generally below the basis cranii in a groove but penetrating into the dorsum sellae. The tip of the notochord was not exposed in the sella. The endo- cranium extended posteriorly above the notochord into the root of the dorsal crest of the carapace, and it also extended back along the lateral margin. The roof of the oral cavity was ridged between the gill pouches, of which ten pairs are generally indicated (11th lateral field orobronchiol plates nasal openings parietal foramen
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dorsal field mouth orobronchiol cavity branchial opening dorsal aorta hyoid arch_

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