. Chordate morphology. Morphology (Animals); Chordata. notochord pericardial cartilage last branchial opening nosoh/pophyseal opening posterior lateral cartilage posterior tectal cartilage nasal capsule anterior tectal cartilage annular cartilage B. subocular arch piston cartilage cornual cartilage 'styloid cartilage (hyoid arch) Figure 5-24. Head and visceral skeletons of the lamprey (partly after Marinelli and Strenger, 1 954). A, entire head and visceral skeleton as seen in lateral view; B, anterior port, enlarged for detail, OS seen in lateral view. Lamprey The lamprey head skeleton consis
. Chordate morphology. Morphology (Animals); Chordata. notochord pericardial cartilage last branchial opening nosoh/pophyseal opening posterior lateral cartilage posterior tectal cartilage nasal capsule anterior tectal cartilage annular cartilage B. subocular arch piston cartilage cornual cartilage 'styloid cartilage (hyoid arch) Figure 5-24. Head and visceral skeletons of the lamprey (partly after Marinelli and Strenger, 1 954). A, entire head and visceral skeleton as seen in lateral view; B, anterior port, enlarged for detail, OS seen in lateral view. Lamprey The lamprey head skeleton consists of an endo- cranium and an extensive "visceral" skeleton (Figures 5-24, 5-25). The endocranium includes a single nasal cap- sule, paired otic capsules, and the side walls and floor of the cranial cavity. The otic capsules are joined above the cra- nial cavity by a synotic tectum. The notochord is much constricted betv/een the otic capsules; it rapidly expands to its spinal proportions posteriorly. It is exposed in the floor of the cranial cavity and thinly covered ventrally by the basis cranii. The basal plate projects posteriorly along the notochord on either side. The anterior tip of the notochord is exposed at the posterior margin of the large hypophyseal fenestra. Anterior to the fenestra is a broad basitrabecular plate lying below the large midline nasal capsule. Behind the neurocranium one or more of the "occipital" arch elements can be viewed as representing the occipital segments of the gnathostome head skeleton. The ninth and tenth cranial nerves exit behind the otic capsule, as does an occipitospinal nerve. The next segmental nerve perforates the base of the first neural arch. The side wall of the neurocranium is joined to the otic capsule at three points: above, anteriorly, and ventroante- riorly. The dorsal opening formed by these connections is filled with connective tissue. The more ventral, larger open- ing is used by the trigeminal, abduce
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