. Chordate anatomy. Chordata; Anatomy, Comparative. 358 CHORDATE ANATOMY and muscles, and by the addition to the nerve fibers of medullary and neurilemma sheaths. A cranial sympathetic ganglion, the ciliary, has developed in association with the oculomotor and profundus nerves. The profundus has now become a branch of the trigeminal. Some of the supraorbital series of lateral-line organs are innervated by fibers of the superficial ophthalmic branch of the fifth nerve, while the remainder are supplied by the superficial ophthalmic of the facialis. The somatic motor nerves of five post-otic myot
. Chordate anatomy. Chordata; Anatomy, Comparative. 358 CHORDATE ANATOMY and muscles, and by the addition to the nerve fibers of medullary and neurilemma sheaths. A cranial sympathetic ganglion, the ciliary, has developed in association with the oculomotor and profundus nerves. The profundus has now become a branch of the trigeminal. Some of the supraorbital series of lateral-line organs are innervated by fibers of the superficial ophthalmic branch of the fifth nerve, while the remainder are supplied by the superficial ophthalmic of the facialis. The somatic motor nerves of five post-otic myotomes unite to form the hypoglossal, which supplies hypobranchial muscles. A thoracic plexus is formed by the union of the nerves immediately posterior to those of the cervical plexus. But the number of nerves which participate varies greatly in different elasmobranchs. In many species the fibers of the cervical and thoracic plexuses unite as a cervico-thoracic plexus. In the region of the pelvic fin is a similar but smaller lumbo-sacral Fig. 317.—Brain of Protopterus, a dipnoan fish, ch, cerebellum; e, epiphysial structures; h, hypophysis; i, infundibulum; tn, mid-brain; se, saccus endolymphaticus; sp, spinal nerves; /, cerebral hemisphere; I—12, cranial nerves. (From Kingsley's "Comparative Anatomy of Vertebrates," after Burckhardt.) Well developed sympathetic ganglia appear in the trunk region, in the vicinity of the dorsal aorta. Their arrangement is metameric, but the anterior and largest is formed by the union of primarily separate ganglia. Each is connected by a ramus commuiiicaiis with a spinal nerve. A longitudinal sympathetic cord or connective is only imper- fectly developed. An intestinal plexus occurs, as in all vertebrates. Amphibia. Amphibia have a relatively simple brain like that of cyclostomes and dipnoans. Olfactory lobes are relatively large and merge without constriction into the cerebral hemispheres. The pallium is thick, and cells ha
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