The pancreas is a thin lobed gland lying between the stomach and duodenum; its duct enters the bile duct which opens on the dorsal wall of the duodenum. The aperture of the larynx opens on the ventral wall of the oesophagus; it is protected by the two arytenoid cartilages and a ring-like cricoid and leads to the two large oval lungs. The lungs have much reticulated walls and are covered externally by peritoneum. The thymus is a small gland lying close behind the angle of each jaw. The thyroid is paired, and each body lies in the angle between the two, i. e. the large and small posterior horns of the hyoid, and adheres to the vena jugularis of its side.
The kidneys are concealed by the fat bodies and genitalia. The former are golden yellow in the fresh state, vascular, and of unknown use. The testes vary in size according to the time of the year. The vasa efferentia run towards the inner border of the kidney: the majority fall into a longitudinal vessel close to that border, while a few may end blindly. From this vessel transverse canals, dilated at their origin, pass outwards, receive tubuli uriniferi, anastomose, and fall into the ureter or Wolffian duct, which runs on the outer margin of the kidney. In the Toads the efferent vessels unite with functional Malpighian corpuscles, represented perhaps by the dilatations (supra) in the Frog. A solid remnant of Muller's duct may be found running forwards on the outer margin of the kidney. It ends blindly. In the Toads this remnant is large, hollow, and uniting with its fellow, opens on the dorsal wall of the cloaca. Each ovary is divided by internal septa into fifteen sacs: the outer surface is lobed. The two oviducts commence by slit-like openings close to the roots of the lungs. At first narrow and straight they become convoluted and glandular, and finally, near their termination, thin-walled and dilated.
Narrowing again, they open on papillae situated anteriorly to the openings of the ureters on the dorsal wall of the cloaca. The kidneys are semilunar glands covered by peritoneum only on their ventral faces. Whitish spots, especially numerous near the efferent veins, mark the position of the nephro-stomata or ciliated funnel-shaped apertures which open into the abdominal cavity and are connected by ciliated tubes with the tubuli uriniferi in the Tadpole (as in Urodeles throughout life); but in the adult, according to Nussbaum, with the reni-portal capillaries. The ureter (Wolffian duct) begins at the anterior end of the kidney, runs along the outer margin, and, in the male, is dilated and glandular just where it quits the kidney, forming the receptaculum seminis. Both ureters open on the dorsal wall of the cloaca separately. The supra-renal capsules are yellow when fresh and e in the median line on the ventral face of the kidneys.
Amphibia, Hoffmann, Bronn's Klass.Und Ordnungen des Thierreichs, vi. Abth. 2. 1873-1878; Huxley, Encyclopaedia Brit. (ed. ix.), i. Anura Batrachia d. Deut-schen Fauna, Leydig, Bonn, 1877.
Rana temporaria.Bell, British Reptiles, London, 1839, p. 84.
The Frog.Ecker and Wiedersheim, Anatomie des Frosches, Brunswick, 3 parts, 1864, 1881, 1882 (with references to literature), in process of translation. A. M. Marshall, Owen's College Course of Elementary Biology i. (ed. 2), 1885. Figures. Atlas of Practical Elementary Biology, Howes, 1885.
Integument.Leydig, Allgemeine Bedeckungen, etc. A. M. A. xii. 1876. Chro-matoblasts and change of colour, Lister, Ph. Tr. 1858, p. 627. Connection of chro-matoblasts with nerves, Ehrmann, SB. Akad. Wien. lxxxiv. Abth. 3. 1882. Nerve-endings. Merkel, Endigungen der sensibeln Nerven in der Haut, Rostock, 1880. Cf. On the Epidermis of Salamander, Pfitzner, M. J. vi. 1880. The periodical moult of cuticle, Knauer, Z. A. ii. 1879.
Digestive tract.Teeth. Tomes, Ph. Tr. 1875; Hertwig A. M. A. xi. (Suppl.), 1874. Intermaxillary gland, Wiedersheim, Z. W. Z. xxvii. 1876. Tongue, organs of Taste. Engelmann, Stricker's Histology (Sydenham Soc), iii. 1873, p. 14. Cf. Z. W. Z. xviii. 1867-69. Glands of Stomach. Partsch, A. M. A. xiv. 1877. Cf. Swiecicki, Arch. f. Physiol. (Pfluger's), xiii. 1876.
Lungs.Schulze, Stricker's Histology (Sydenham Soc), ii. 1872, p. 72.
Heart, vessels, carotid gland.Boas, M. J. vii. 1881, p. 488; cf. especially pp. 502 and 540; M. J. viii. 1882. Sabatier, Etudes sur le Coeur, etc., Paris, 1873; Fritsch, Archiv. f. Anat. und Physiol. 1869.
Spleen.Phisalix, A. Z. Expt. (2) iii. 1885.
Lymphatic system.Langer, SB. Akad. Wien. viii. Abth. i. 1866; iv. Abth. i. 1867.
Urogenital system.Spengel, Arb. Zool. Zoot. Inst., Wurzburg, iii. 1876. Connections of nephrostomata. Nussbaum, Z. A. iii. 1880.
Spermatogenesis.Blomfield, Q. J. M. xxi. 1881. Albumen glands of Oviduct. Loos, Z. W. Z. xxxv. 1881.