. The Bashford Dean memorial volume :. Fishes; Sharks; Fishes, Fossil. 476 Bashford Dean Memorial Volume Brohmer (1909) described briefly the cranial nerves of a 25'min. embryo. The account of the cranial nerves by AUis (1923) is, as the author states, incomplete. The general plan of the cranial nerves of vertebrates is best revealed in their em' bryos. For the embryo of Scyllium, this plan is set forth diagrammatically in Text'figure 117. A somewhat comparable figure for Chlamydoselachus, based on a single embryo, is supplied by Text'figure 118, after Brohmer. TUC. hXTh Text'figure 117. Diagr
. The Bashford Dean memorial volume :. Fishes; Sharks; Fishes, Fossil. 476 Bashford Dean Memorial Volume Brohmer (1909) described briefly the cranial nerves of a 25'min. embryo. The account of the cranial nerves by AUis (1923) is, as the author states, incomplete. The general plan of the cranial nerves of vertebrates is best revealed in their em' bryos. For the embryo of Scyllium, this plan is set forth diagrammatically in Text'figure 117. A somewhat comparable figure for Chlamydoselachus, based on a single embryo, is supplied by Text'figure 118, after Brohmer. TUC. hXTh Text'figure 117. Diagram of the segmentation of the head in an embryo of Sc-yWium canicula. The myotomes are longitudinally striated, the nerves black, and the scleromeres dotted. The cartilaginous visceral arches, also the optic capsule and the nasal sac, are represented by dotted outlines. I'VI, gill-slits; I-ll, somites, prootic from 3 forwards, and metaotic from 4 backwards; a, auditory nerve; ah, abducens nerve; ac, auditory capsule; ah, anterior head cavity; c, coelom in lateral plate mesoblast; cr, limit of cranial region; /, facial nerve; gl, glossopharyngeal nerve; ha, hyoid cartilaginous arch; hm, hypoglossal muscles from myotomes of somites 6, 7, 8; h)i, hypoglossal complex nerve; !a, lamina antotica; m, mouth; ml, second metaotic myotome; m6, sixth metaotic myotome; ma, mandibular cartilaginous arch; mb, muscle bud to pectoral fin; nc, nasal capsule, continuous with trabecula behind; aal and aa2, first and second occipital arches of segments 6 and 7; om, oculomotor nerve; prf, profundus nerve; scl, sclerotome of segmentlO; spl, vestigial dorsal root and ganglion of first spinal nerve; sp2, second spinal; t, trochlear nerve; tr, trigem- inal nerve; v, complex root of vagus nerve; vgl, vestigial dorsal root and ganglion of segment 7; vc, ventral coelom extending up each visceral bar; vr, ventral nerve root of segment 6, supplying second metaotic myotome and hypoglossal muscle; vs, Umit of
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