MAESUPIALIA 



21 



Order II. MARSUPIALIA.i 



(Didelphia Blainville ; Metatheria Huxley.) 



Herbivorous and carnivorous animals of highly diversified heterodont dentition. 

 Pectoral arch with reduced coracoid and without precoracoid, pelvis with marsupial 

 bones. Nipples usually enclosed in a skin fold, which forms a sack in which the 

 young, incompletely developed at birth, are carried for a considerable period. 



The marsupials constitute a large division of Mammalia, comprising carni- 

 vorous and insectivorous types as well as hoofed and rodent-like forms. These 

 manifold variations are displayed not only in the dental but also in the skeletal 

 structure. The brain is small, and the 

 olfactory and optic lobes and the cerebellum 

 are not covered by the smooth hemispheres 

 of the cerebrum. The nasals are large, the 

 jugal arch complete, and the orbits are open 

 posteriorly. The alisphenoid takes part in 

 the formation of the auditory capsule, less 

 commonly the mastoid and semicircular tym- 

 panic. The hard palate is always perforated 

 with larger or smaller foramina. The pos- 

 terior angle of the lower jaw is inflected. 



The teeth resemble in some respects 

 those of herbivores and rodents, and in 

 others insectivores and carnivores. Among 

 the former the number of /, F and C teeth 

 are greatly reduced, but to counterbalance 

 this deficiency one of the / is very strongly 

 developed in both jaws. The latter type has 

 a complete set of teeth in which there are, 

 as a rule, as many as -f- / teeth. The C are fig. 26. 



very powerful, often having two roots. a, TncJwsurus, hind foot with five subequal 

 Ai.vTi p -lix J toes. B, if acronus, I. -III. toes reduced. (After 



Also, the Jr are of very simple structure and doIIo.) ' -^ ' 



medium size, only the most posterior one 



being large and often highly specialised. The majority of 31, found in groups 



of four, are either secodont, bunodont or lophodont. Dental succession is 



limited to the last P. The jaw in the embryos of existing Marsupials contains 



the rudiments of more teeth than occur in the adult. 



^ Amegkino, F., Los Diprotodontes del orden de los Plagiaulacoideos. Anal. Museo Nacion. 

 Buenos Aires, vol. ix., 1903. — Cope, E. D., The Tertiary Marsupialia. Amer. Naturalist, 1884. — 

 Goodrich, E. S., Mammalia from the Stonesfield Slate. Quart. Journ. Micros. Sci., vol. xxxv. — 

 Gregory/, W. K., The orders of mammals. Bull, Amer. Mus. Nat. Hist., vol. xxvii., 1909, p. 162- 

 2Zl.— Marsh, 0. C, Amer. Journ. Sci., 1880, vol. xx. ; 1881, vol. xxi. ; 1889, vol. xxxviii. ; 1892, 

 vol. xliii. — Osborn, H. F., Proc. Acad. Nat. Sci. Philad., 1887-88. — Journ. Acad. Nat. Sci. 

 Philad., vol. ix. , 1888. — Evolution of the mammalian molar teeth. New York, 1907. — Oimn, R., 

 Monograph of fossil Mammalia of the British Mesozoic formations. Palaeontogr. Soc, 1871. — 

 E,esearches on the fossil remains of the extinct mammals of Australia with a notice of the extinct 

 marsupials of England. Loudon, 1877. — Sinclair, W. J., Marsupialia of the Santa Cruz beds. 

 Eept. Princeton Univers. Exped. to Patagonia, vol. iv. part iii., Y'ibQ. ^Thomas, 0., On the homo- 

 logies and succession of the teeth in the Dasyuridae. Phil. Trans. Roy. Soc, 1887, vol. 178 B. — ■ 

 Broom, J?., Bull. Amer. Mus. Nat. Hist., 1914, vol. xxxiii. pp. 115-34. — Mattheiv, W. D., ibid., 

 1916, vol. xxxv. pp. ^77 -500. — Wood, II. E., Sparassodonts. Bull. Amer. Mns. Nat. Hist., 1924, 

 vol. li. p. 77. — Woodivari/, A. S., Diprotodon, Geol. Mag., 1907, p. 337. — Wealden Teeth, Q. Journ. 

 GeoL Soc, 1911, p. 278.— Triconodon, Proc. Geol. Assoc, 1912, vol. xxiii. p. 100. 



