. Chordate morphology. Morphology (Animals); Chordata. basilar artery posterior commissure ^cerebellum lateral-line lobe membranous roof. anterior commissure preoptic recess hypothalamus fourth ventricle spinal cord saccus vosculosus pituitary Figure 13-12. Broin and cranial nerve roots of Squa/us A, dorsal; B, ventral; C, medial view right half. of The cranial nerves of the lamprey are in general compar- able to those of the gnathostomes (Figure 13-16). The ol- factory consists of many fibers. The optic nerves cross with- out complication; the oculomotor is comparable to that of the higher fo
. Chordate morphology. Morphology (Animals); Chordata. basilar artery posterior commissure ^cerebellum lateral-line lobe membranous roof. anterior commissure preoptic recess hypothalamus fourth ventricle spinal cord saccus vosculosus pituitary Figure 13-12. Broin and cranial nerve roots of Squa/us A, dorsal; B, ventral; C, medial view right half. of The cranial nerves of the lamprey are in general compar- able to those of the gnathostomes (Figure 13-16). The ol- factory consists of many fibers. The optic nerves cross with- out complication; the oculomotor is comparable to that of the higher forms, but the trochlear does not decussate; the nerve of either side goes to the superior oblique muscle of the same side. There is doubt as to vv-hether there is a nerve since the nerve in question comes out along with the fifth and is said to contain at least some oculomotor fibers. The profundus division of the fifth arises from the brain wall independent of the combined maxillary and mandibu- lar branch. Their ganglia are in part separate. Unlike the other fishes, the lamprey lacks a superficial ophthalmic division of the fifth and seventh nerves, but the lateral-line sensory system is only poorly developed. The fifth and seventh nerves are closely associated, making it difficult to identify distinct lateral-line branches similar to those of other fishes. The seventh and eighth nerve roots are close together and both perforate the otic capsule, the eighth entering the capsule, the seventh passing down through the anterior capsule wall. The glossopharyngeal and vagus are similar to those of other fishes with lateral-line and bran- chial arch divisions. Each branchial nerve has typical pre- and post-trematic divisions. The vagus also continues into the body as the visceral component of the parasympathetic system. The hypoglossal nerve is a derivative of the more anterior spinal nerves and as such is like that in other fishes. 396 THE NERVOUS SYSTEM. Please note that the
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