. Comparative anatomy. Anatomy, Comparative. 624 COMPARATIVE ANATOMY Head Segments According to Beard Dorsal nerve root Branchial cleft Nature of sense-organ of cleft Ganglion Head cavity Ventral nerve root I Olfactory None Olfactory organ Olfactory None None II Radix longa of ciliary None, or hypo- Branchial Ciliary First Oculomotor III ganglion Trigeminus physis Mouth Branchial Gasserian Second Trochlear IV > V S Facial â ] Absent Branchial Branchial Branchial â Facial Third ? Abducens None VI Auditory None Auditory organ Auditory None None VII Glosso- pharyngeal I St branchial Branchial
. Comparative anatomy. Anatomy, Comparative. 624 COMPARATIVE ANATOMY Head Segments According to Beard Dorsal nerve root Branchial cleft Nature of sense-organ of cleft Ganglion Head cavity Ventral nerve root I Olfactory None Olfactory organ Olfactory None None II Radix longa of ciliary None, or hypo- Branchial Ciliary First Oculomotor III ganglion Trigeminus physis Mouth Branchial Gasserian Second Trochlear IV > V S Facial â ] Absent Branchial Branchial Branchial â Facial Third ? Abducens None VI Auditory None Auditory organ Auditory None None VII Glosso- pharyngeal I St branchial Branchial Glosso- pharyngeal ? None VIII Vagus I 2nd branchial Branchial Vagus I None None IX) 3d, 4th, & (Branchial ) Vagus II, Vagus II, III, and IV 5th bran- chial < Branchial (Branchial \ III, and None None In cyclostome embryos, Kupffer ('95) found thirteen such epibranchial sense organs, five anterior to the facial ganghon and seven posterior. Six of these are associated with the visceral branches of the vagus nerve. Kupffer's results, however, have never been confirmed, and relatively N. FACIALIS N. TRIGEMINUS ? N. GLOSSOPHARYNGtUS EAR/ ,N. VAGUS /LATERAL LINE NERVE. NOTOCHORD NOSE / EPIBRANCHIAL GANGLIA (x-an) HYPOPHYSIS Fig. 518.âA diagram of the head of a Petromyzon (ammocoetes) embryo seen from the left side showing the series of epibranchial placodes in solid black. Beard and Kupffer have suggested that such placodes or "epibranchial sense organs" might be used as criteria of the primitive segmentation of the head. (Redrawn after Kupffer.) few schemes of cephalic segmentation make use of epibranchial ganglia as criteria of metamerism. In the attempt to compare a head segment with a trunk segment, a number of mistakes have been made. Gegenbaur's homology of a skeletal visceral arch with a rib is invalidated by the fact that the two. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - c
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