. Comparative anatomy. Anatomy, Comparative. Sup. rectus^ ^^_ oculomotork Tf«OCMLEABIS^_ M. OSLIQUUS SUR. EXT. RECTUS— —. Fig. 219.—Diagrams of the eye muscles of man. A shows the left eye-ball and associated muscles viewed from the outer side. B is the left eye-ball with associated muscles and nerves viewed from the median side. (Redrawn after "Warren and Carmichael, Coiirtesy of Houghton Mifflin & Co.) Hypobranchial muscles, lacking in amphioxus, first appear in cyclo- stomes. They arise from postbranchial myotomes which send myotomic buds ventrally and anteriorly below the gills as
. Comparative anatomy. Anatomy, Comparative. Sup. rectus^ ^^_ oculomotork Tf«OCMLEABIS^_ M. OSLIQUUS SUR. EXT. RECTUS— —. Fig. 219.—Diagrams of the eye muscles of man. A shows the left eye-ball and associated muscles viewed from the outer side. B is the left eye-ball with associated muscles and nerves viewed from the median side. (Redrawn after "Warren and Carmichael, Coiirtesy of Houghton Mifflin & Co.) Hypobranchial muscles, lacking in amphioxus, first appear in cyclo- stomes. They arise from postbranchial myotomes which send myotomic buds ventrally and anteriorly below the gills as far forward as the mouth. The development and nerve relations of this hypobranchial musculature prove that it is the homologue of the tongue and throat muscles, which in higher vertebrates, are innervated by the twelfth nerve, the hypoglossal. Cyclostomes, however, have no true tongue. The hypobranchial muscles function as a part of the lateral trunk muscles. (Fig. 218.) A further evolution of muscles also appears in elasmobranchs. The embryos of this group provide a clue to the history of the eye muscles, by demonstrating that the differentiation of the three anterior myotomes into the six eye muscles involves primarily a longitudinal sphtting of the myotomes into dorsal and ventral moieties such as happens also in the first and second post-otic myotomes of cyclostomes. The facts suggest that the splitting occurred along the series of lateral line sense organs, which at one time may have included the lens of the eye and the ear capsule. Each of the two divisions of the first myotome spHts again lengthwise, thus making the four eye muscles innervated by the oculo-. 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 Neal, Herbert V. (Herbert Vincent), 1869-1940; Rand, Herbert W. (Herbert Wilbur), 1872-19
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