322 
HENRY ORR. 
EXPLANATION OF PLATES XXVII, XXVIII, & XXIX, 
Illustrating Mr. Henry Orr’s paper “Note on the Develop- 
ment of Amphibians, chiefly concerning the Central 
Nervous System ; with Additional Observations on the 
Hypophysis, Mouth, and the Appendages and Skeleton of 
the Head.” 
Where a number of figures represent sections of the same individual embryo, 
all those figures have the same letter affixed to their numbers. 
All figures of sections have been drawn with the Abbey camera lucida and a 
Zeiss’s microscope, so that in figures magnified to the same degree the size of 
the parts may be directly compared. (Z. 2, A, means Zeiss’s ocular 2, and 
objective A, &c.) 
Index Letters. 
A. C. Anterior commissure of fore-brain. A. F. Anterior medullary fold. 
A. F'. Anterior band of nerve-fibres, continuous with the lateral bands, L. F. 
a. M. P. Anterior medullary plate. B. Ey. Basi-hyobranchial plate of 
cartilage. Bl. Region of the blastopore, hi. Balancers, c. b. Cartilaginous 
bar connecting dorsally the cartilaginous gill-arches. Ch. Optic chiasma 
united with the anterior band of nerve-fibres (A. F'.). d. Dental rudiments. 
E. Ear. Ep. Epiblast. Eph. Epiphysis cerebri. Ey. Eye. F. B. Fore- 
brain. G — g. See explanation of Eigs. 2 a — 5 d. H. B. Hind-brain. H. C. 
Head cavity. Hph. Hypophysis. Et. Heart. Eyp. Hypoblast. In. In- 
fundibulum. L. Lens of eye. L. F. Primary longitudinal fibres of central 
nervous system ; L. F'. the same in the region of the thalamencephalon. 
M. Mouth-fusion or mouth. m. and ml. Pterygoid and branchial muscles. 
M. B. Mid-brain. Md. Medulla spinalis. Mes. Mesoblast. M. F. Lateral 
medullary fold. mk. Meckelian cartilage. M. P. Lateral medullary plate. 
N. Notochord or rudiment of the same. Na. Nasal sac. n. I , n. II — n. X. 
Olfactory, optic, and succeeding cranial nerves, o.f. Opercular fold of the 
hyoid arch. o.g. Optic groove, o.p". Posterior wall of the optic stalk. 
p. Lateral cartilaginous process of the quadrate at the base of the balancer. 
P. C. Posterior commissure of the brain, p. g. Rudiment of the pectoral 
girdle. PE. Pharyngeal cavity. So. Somatopleure of mesoblast. Sp. 
Splanchnoplcure of mesoblast. St. Corpora striata. Hr. Trabecula: cranii. 
T. F. Transverse nerve-fibres forming a continuous ventral commissure. Th. 
Rudiment of the thyroid gland, w. E. B. Floor of hind-brain, x — y. See 
explanation in text, p. 319. Y. Yolk. I — V. Hyoid and branchial clefts. 
V — V. Cartilaginous gill-arches. 
