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==Plate 13==

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Illustrating Dr. Milnes Marshall's Paper on the " Morphology of the Vertebrate Olfactory Organ." 

Each figure has been drawn from a single section by the aid of a Hartnack camera. The numbers attached indicate, in diameters, the magnifying power employed in each case. The majority of the figures are of a semi-diagrammatical nature, the mesoblast being in nearly all cases omitted for the sake of clearness; the outlines are, however, strictly accurate in all cases. Figures 21, 22, 27, and 28 are drawn from sections kindly lent me for the purpose by Mr. Balfour ; the rest are from specimens of my own preparation. 

===Alphabetical List of References===

ah Alimentary canal. aV . Anterior prolongation of alimentary canal. aor. Dorsal aorta. a. r. Anterior root of a spinal nerve. mtcl. Auditory vesicle. b. a. Branchial artery. br. 1. First branchial arch. 
br. 2. Second branchial arch. c. h. cerebral hemisphere. f. b. forebrain, g. gill. h. 2. Second head-cavity. h . b. Hindbrain. hy. Hyoid arch. inf. Infundibulum, I. c. Lachrymal cleft. m. b. Midbrain. Mn. Mandibular arch. m. p. Muscle plate. 3f.v. Maxillary arch. u. Notochord. o. c. Optic cup or eye. olf. Olfactory pit. ol. V. Olfactory vesicle or lobe. r. i. Inferior rectus muscle. r. s. Superior rectus muscle. Sch. Schneiderian folds. sp. Spinal cord. tr. Trabecula3 cranii. v. c. Visceral cleft. I. Olfactory nerve. II. Optic nerve. III. Third or oculomotor nerve. V. Trigeminal nerve. V a. Opiithalmic branch of the trigeminal nerve, or ramus ophthalmicus profundus. V 3. Inferior maxillary branch of the trigeminal nerve. VII. Facial nerve. VII a. Ophthalmic branch of the facial nerve, or ramus ophthalmicus superficialis. VIII. Auditory nerve. IX. Glossopharyngeal nerve. X. Vagus or pneumogastric nerve. 


Fig. 1. — Longitudinal and horizontal section through the head of a fifty-four hours' chick embryo, showing early stage in the formation of the olfactory pits, also the visceral clefts with their communication with the exterior. Picric acid, x 35 diameters. 

Fig. 2. — Longitudinal and vertical section through the fore part of the head of a sixty-four hours' chick embryo, showing olfactory nerve and pit. Picric acid, x 27 diam. 

Fig. 3. — Longitudinal and vertical section through the head of a sixty-seven hours' cliick embryo, showing the olfactory pit, the maxillary, mandibular, hyoideau, and first three branchial arches, with the intervening clefts. Picric acid, x 20 diam. 

Figs. 4—6. — Longitudinal and vertical sections through the head of a ninety-six hours' chick. Picric acid, x 15 diam. 

Fig. 4. — The most superficial of the series ; shows the maxillary, mandibular and hyoidean arches, with their intervening clefts, and the trigeminal, facial, and auditory nerves. 

Fig. 5 shows, in addition, the olfactory pit and the distal end of the olfactory nerve. 

Fig. 6 shows the third, glossopharyngeal and vagus nerves. 

Figs. 7 and 8. — Longitudinal and vertical sections through the cerebral hemispheres and nasal region of a six-day chiek embryo. Picric acid. X 15 diam. 

Fig. 7 shows whole length of olfactory nerve. 

Fig. 8 shows ganglion at root of origin of olfactory nerve, also internal projection of hemisphere at this point. 

Fig. 9. — Longitudinal and vertical section through the nasal region of a 
seven-day chick embryo, showing whole length of olfactory nerve, and commencing rudiment of olfactory lobe. Picric acid, x 15 diam. 

Fig. 10. — About half of a transverse section through the forebrain of a four-day duck embryo, showing the olfactory nerve and pit. Picric acid. X 50 diam. 

Figs. 11 and 12. — Tranverse sections through the anterior part of the head of an eighty-hours' chick embryo, passing through the cerebral hemispheres, and the olfactory pits and nerves. Picric acid, x 27 diam. 

Fig. 11 shows on left side the origin of the olfactory nerve. 

Fig. 12 shows on right side the distal end of the olfactory nerve. 

Fig. 13. — Longitudinal and horizontal section through the head of a dogfish embryo of stage k, showing early stage in development of the olfactory pits. Chromic and osmic acids, x 20 diam. 

Fig. 14. — Transverse section through the anterior extremity of the head 
of a dogfish embryo of stage k, showing the forebrain, the olfactory pits and 
nerves. Chromic and osmic acids. X 20 diam. 

Fig. 15. — Longitudinal and vertical section through the head of a dogfish 
embi-yo of stage m, showing the olfactory pit and nerve. Chromic and 
osmic acids, x 20 diam. 

Fig. 16. — Longitudinal and vertical section through the head of a dogfish 
embryo of stage M, showing the olfactory pit, the mandibular, hyoid and 
branchial arches. Chromic and osmic acids, x 20 diam. 

Figs. 17 and I8. — Longitudinal and vertical sections through the head of a dogfish embryo of stage o. Chromic and osmic acids, x 20 diam. 

Fig. 17 shows olfactory pit and nerve. 

Fig. I8 shows olfactory pit, with Schneiderian fold, olfactory nerve, forebrain, hyoid and branchial arches. 


{{Marshall1879 figures}}