MARSUPIALIA. 



299 



are adapted, the first for cropping the foliage of 

 the gum-trees (Eucalypti) and similar trees, 

 and the others for bruising and masticating the 

 same. The grinding surface of the molars ge- 

 nerally presents four blunt tubercles. 



The Koala resembles in its dentition and in 

 its diet and arboreal life the Phalangers and 

 Petaurists. In the lower jaw the absence of 

 teeth between the two large procumbent incisors 

 and the false molars is constant ; in the upper 

 jaw, however, the lateral or posterior incisors 

 begin to exhibit the same diminution of size as 

 the corresponding teeth in the lower jaw of 

 some of the Phalangers, while the two anterior 

 upper incisors present a proportional increase ; 

 the canines correspond in feebleness and form 

 with the small incisors. In the Wombat, the 

 defective development to which the teeth be- 

 tween the incisors and molars are subject in 

 the Marsupial tribe, has reduced the dental for- 

 mula of both jaws to the rodent type ; but the 

 shape, comparative shortness, and procumbent 

 position of the two large inferior incisors, and 

 the three-sided figure of the opposing pair 

 above, bespeak the marsupial character of which 

 this genus offers so extreme a modification. 

 The grinders, however, agree with those of the 

 herbivorous rodents in the absence of fangs, 

 arising from the uninterrupted growth and ossi- 

 fication of their formative pulps ; they offer 

 also in both jaws an extreme degree of the cur- 

 vature which characterises the molars of some 

 herbivorous Rodents, as the Guinea-pig, and 

 the great extinct gliriform Pachyderm, called 

 Toxodon ; but their chief distinctive peculi- 

 arity is the marsupial excess of number already 

 mentioned. 



With respect to the modifications of the 

 teeth of the herbivorous Marsupials, it need 

 only here be observed that the grinding surface 

 of the true molars in the Kangaroos most re- 

 sembles that which characterizes the same teeth 

 in the Tapir, Dinothere, and Manatee. 



No Marsupial pcssesses teeth composed of 

 an intermixture of layers of dentine, enamel 

 and cement throughout the crown, but the ex- 

 ternal layer of coronal cement is very conspi- 

 cuous in transverse sections of the teeth of the 

 Marsupials, viewed with the microscope, and 

 forms a thick layer on the outside of the crowns 

 of the teeth in the genera Macropus, Ph(<scol- 

 arctuii, and Phascolomys. 



The modifications of the tongue and soft 

 palate have already been noticed. In two 

 species of Marsupials I have detected cheek- 

 pouches. In the Koala they are wide and 

 shallow, situated one on each side of the upper 

 lip ; the orifice is opposite the first superior 

 premolar, and leads forwards above a horizontal 

 fold of the mucous membrane which attaches 

 the upper lip to the side of the intermaxillary 

 bone, separating this part of the cheek-pouch 

 from the mouth. In the Perameles Ingot is 

 there are also two small fossse, one on the in- 

 side of each cheek, about four lines in diameter, 

 and lined by a very distinct white epithelium. 



The fauces are wide in the Zoophagous, but 

 narrow in the Entomophagous and Phytopha- 

 gous Marsupials. 



Alimentary canal, The (Esophagus in passing- 



through the chest recedes from the spine as it 

 approaches the diaphragm, and is loosely con- 

 nected with the bodies of the dorsal verte- 

 bra by a broad duplicature of the serous 

 membrane of the posterior mediastinum. In 

 the Phalangers the oesophagus terminates in the 

 stomach almost as soon as it has pierced the 

 diaphragm ; in the Opossums it is continued 

 some way into the abdomen ; in the Didelphys 

 Virginiana, for example, for the extent of an 

 inch and a half; in Did. brachyuru, for half 

 an inch. In the Kangaroos the abdominal 

 portion of the cesophagus is of still greater 

 extent ; 1 have observed it five inches long in 

 a male Macropus major. 



The inner surface of the cesophagus is gene- 

 rally smooth, or disposed in fine longitudinal 

 plaits ; but in the Virginian Opossum the ter- 

 minal part of the oasophagus presents many 

 transverse folds of the lining membrane analo- 

 gous to, but relatively larger than those in the 

 Lion and other Felines. I have not met with 

 a like structure in the Phalangers nor in any 

 other genus of Marsupials ; what is more re- 

 markable is that the transverse cesophageal rugae 

 are not developed in the carnivorous Dasyures 

 or Pkascogales, where analogy would lead one 

 to expect them, rather than in the insectivorous 

 Opossums. 



The stomach presents three leading modifica- 

 tions of structure in the Marsupialia; it is either 

 simple, as in the Zoophagous, Entomophagous, 

 and Carpophagous tribes; or is provided with a 

 cardiac glandular apparatus, as in the Koala and 

 Wombat; or is complicated by sacculi, as in the 

 Poephagans. 



It might have been expected that the stomach 

 would have exhibited some modifications in 

 the development of the left or cardiac extremity 

 corresponding with the differences of food and 

 dentition observable in the large proportion of 

 the Marsupial order, in which this viscus pre- 

 sents its simple condition ; but this is not the 

 case : the form of the stomach is essentially the 

 same in the carnivorous Dasyure, the insecti- 

 vorous Bandicoot, and the leaf-eating Phalan- 

 gers. It presents a full, round, ovate, or 

 sub-triangular figure, with the right extremity 

 projecting beyond and below the pylorus ; the 

 longitudinal diameter seldom exceeds the ver- 

 tical or transverse by more than one- third ; often, 

 as in Phascogale and Dasyurus viverrinus, by 

 only one-fourth of its own extent ; and the 

 cesophagus enters at the middle of the lesser 

 curvature, or sometimes nearer the pylorus, but 

 always leaves a large hemispherical cul-de-sac 

 on the left side. Daubenton has given illustra- 

 tions of this characteristic form of the stomach 

 in different species of Didelphys; it is here 

 figured as it exists in the Phascogale (fig. 122). 

 The stomach is relatively much more capacious 

 in the carnivorous Marsupials than in the car- 

 nivorous Placentals. Some slight modifica- 

 tions occur in the disposition of the lining 

 membrane ; thus in the Phascogale I observed 

 a series of very thick ruga} radiating from the 

 middle of the upper part of the coecal end of 

 the stomach, some of which were continued 

 along the lesser curvature to the pylorus. Dr. 

 Grant found, in the Perameles nasttta, that " the 



