PANCREAS. 243 



In Mammals the liver may always be derived from a ground- 

 form consisting of two lobes, but in most cases it becomes further 

 subdivided, so that in some cases there may be as many as six or 

 seven lobes (e.g. Dog, Weasel). The right primary lobe is always 

 the longest, and in it the gall-bladder, when present, lies partially 

 embedded. 



Pancreas. 



As already mentioned, this organ also arises from the proximal 

 portion of the small intestine, and comes into close relation with 

 the liver. Its point of origin from the intestine corresponds to the 

 aperture of the pancreatic duct, which penetrates the entire 

 organ. 



With the exception of certain Fishes (e.g. Cyclostomi and 

 many Teleostei) and Perennibranchiates (Siren and Proteus), a 

 pancreas is always present in Vertebrates. Varying much in form 

 and size, it early gives rise to a band-shaped or more or less 

 lobulated organ, usually lying in the fold of the duodenum. Its 

 duct frequently becomes united with that of the liver (Fig. 197, P 1 , 

 Dc l , Z)c 2 ), or there may be several independent ducts opening into 

 the intestine (e.g. Birds, Crocodilia, Emydse, and some Mammalia). 



BIBLIOGRAPHY. 



AYERS, H. Beitrage zur Anat. u. Physiol. der Dipnoer. Jenaische Zeitschr. f. 



Naturwissenschaft. Bd. XVIII. (N.F. Bd. XL), 1885. 

 BATTME. Odontologische Forschungen, I. Leipzig, 1882. 

 BORN, G. Ueber die Derivate der embryonalen Schlundbogen, &c. Arch. f. inikr. 



Anat. Bd, XXII. 1883. 



CATTANEO, G. Istologia e sviluppo dell' apparato gastrico degli uecelli. Milano, 1884. 

 DOBSON, G. E. On Peyer's Patches. Journ. Anat. 1884. 

 DOHRN, A. Studien zur Urgeschichte des Wirbelthierkorpers. MUM. aus d. zool. 



Station zu Neapel. Bd. V. Heft 1. Bd. VI. Heft 1, 1884. (These include an 



account of the thyroid gland of Elasmobranchs, Petromyzon, Amphioxus, and 



Tunicata. ) 

 EDINGER, L. Ueber die Schleimhaut des Fischdarmes, &c. Arch. f. mikr, Anat. 



Bd. XIII. 1877. 

 FISCHELIS, PH. Beitrage zur Kenntniss der Glandula thyreoidca u. Glandula thymus. 



Arch. f. mikr. Anat. Bd. XXV. 1885. 

 FLOWER, W. H. Lectures on Odontology. Med. Times and Gazette, 1871. Lectures 



on the Comparative Anatomy of the Organs of Digestion of the Mammalia. Ibid. 



Feb. to Dec., 1872. 



FORBES, W. A. On theBursa Fdbricii in Birds. Proc. Zool. Soc. 1875. 

 GADOW, H. Versuch einer vergl. Anatomie des Verdauungssystemes der Vogel. 



Jenaische Zeitschr. Bd. XIII. N.F. VI. 

 HENSEL, R. Ueber Homologieen und Varianten in den Zahnformen einiger Sauge- 



thiere. Morphol. Jahrb. Bd. V. 1879. 

 HERTWIG, 0. Ueber das Zahnsystem der Amphibien und seine Bedeutungfilr die 



Genese des STcelcts der Mundhohle. ArchTf. mikr. Anat. Bd. XI. 1874. 

 His, W. Anatomie menschlicher Embryonen. Leipzig, 1880-1885. 

 HUXLEY, T. H. Tegumentary Organs. Encycl. of Anat. and Physiol. Vol. V. (See 



also Quart. Journ. Micros. Science, 1853.) 

 LEYDIG, T. Ueber die Kopfdrusen einheimischcr Ophidier. Arch. f. mikr. Anat. 



Bd. IX. 1873. 



B 2 



