. Comparative anatomy. Anatomy, Comparative. 264 COMPARATIVE ANATOMY the gill cartilages, and are differentiated into levators, depressors, and constrictors of the gills. The lateral trunk muscles of cyclostomes strikingly resemble those of amphioxus. In the region of the body cavity, on the ventral side, an external layer of oblique muscles is differentiated. The most important evolutionary advance, however, appears in the differentiation of six eye muscles. Paired eyes first appear in this group, and with them the same six eye muscles as in all vertebrates up to man. All six are formed from
. Comparative anatomy. Anatomy, Comparative. 264 COMPARATIVE ANATOMY the gill cartilages, and are differentiated into levators, depressors, and constrictors of the gills. The lateral trunk muscles of cyclostomes strikingly resemble those of amphioxus. In the region of the body cavity, on the ventral side, an external layer of oblique muscles is differentiated. The most important evolutionary advance, however, appears in the differentiation of six eye muscles. Paired eyes first appear in this group, and with them the same six eye muscles as in all vertebrates up to man. All six are formed from the first three embryonic myotomes. It is generally assumed that, like the eye muscles of higher vertebrates, they are innervated by the 3rd, 4th, and 6th cranial nerves. Since in cyclostomes the fourth myo- tome of the embryo forms the first permanent trunk myotome, all the myotomes of the embryo persist in the adult. Of none of the higher vertebrates is this true. (Figs. 218, 219, 220.). Sup. rectus^ ^^_ oculomotork Tf«OCMLEABIS^_ M. OSLIQUUS SUR. EXT. RECTUS— —. 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), 1872-1960. Philadelphia : P. Blakiston's Son
Size: 2086px × 1198px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookpublisherphi, booksubjectanatomycomparative
