MARSUPIATA. 



MARSUPIATA. 



The specimen of the half-jaw of the Tbylacothere examined by H. 

 Valenciennes, like that which wa transmitted to Curler, presents the 

 inner lurface to the obeerrer, and exhibit* both the orifice of the 

 dental canal and the symphyais in a perfect state. The foramen in 

 toe fossil it situated relatively more forward than in the recent 

 OpOMum and Dasyure, or in the Placenta! Jnieclirora. but has tlie 

 lame place as in the marsupial genus Hyptiprymntu. The symphynis 

 is long and narrow, and is continued forward in the Fame line with 

 the grntly convex inferior margin of the jaw, which thus tapers 

 gradually to a pointed anterior extremity, precisely as in the jaws of 

 the Marsupial Jnxclirora. In the relative length of the symphysis, 

 its form and position, the jaw of the Thylacotlierium precisely corres- 

 ponds with that of the Didrlphyt. 



In addition however to these proofs of the mommiferous nature of 

 the Stonesfield remains, and in part of their having belonged to Harm- 

 fiata. Professor Owen stated that the jaws exhibit a character hitherto 

 unnoticed by the able anatomists who have written respecting them, 

 bat which, if co-existent with a convex condyle, would serve to prove 

 the marsupial nature of a fossil, though all the teeth were wanting. 



In recent marsupials the angle of the jaw is elongated and bent 

 inwards in the form of a process, varying m shape and development 

 in different genera. In looking therefore directly upon the inferior 

 margin of the marsupial jaw, we see, in place of the edge of a vertical 

 plate of bone, a more or less flattened triangular surface or plate of 

 bone extended between the external ridge and the internal process or 

 inflected angle. In the Opossum this process is triangular and 

 trihedral, and directed inwards with the point slightly curved upwards 

 and extended backwards, in which direction it is more produced in 

 the small than in the large species of Didclphyr. 



Now, observed Professor Owen, if the process from the angle of 

 the jaw in the Stonesfield fossil had been simply continued back- 

 wards, it would have resembled the jaw of an ordinary placenta! 

 carnivorous or insectivorous mammal ; but in both specimens of 

 Ttiylacotherium, the half jaws of which exhibit their inner or mesial 

 surfaces, this process presents a fractured outline, evidently proving 

 that when entire it must have been produced inwards or mesially, as 

 in the Opossum. 



Professor Owen then described in great detail the structure of the 

 teeth, and showed, in reply to M. De BlaiuviUe's second objection, that 

 they are not confluent with the jaw, but are separated from it at their 

 base by a layer of matter of a distinct colour from the teeth or the 

 jaw, but evidently of the same nature as the matrix ; and secondly, 

 that the teeth cannot be considered as presenting nn uniform com- 

 pressed tricuspid structure, and being all of one kind, as M. De Blain- 

 ville states, but must be divided into two series as regards their 

 composition. Five if not six of the posterior teeth are quinque- 

 cuspidate, and are molures vcri; some of the molares spurii are 

 tricuspid, and some bicuspid, as in the Opossums. An interesting 

 result of this examination is the observation that the five cusps of the 

 tuberculate molars are not arranged, as had been supposed, in the 

 same line, but in two pairs placed transversely to the axis of the jaw, 

 witli the fifth cusp anterior, exactly as in the JJidclphy*, and totally 

 different from the structure of the molars in any of the Phoca, to 

 which these very small Mammalia have been compared : and in 

 reference to this comparison Professor Owen again called attention 

 to the value of the character of the process continued from the angle 

 of the jaw, in the fossils, as strongly contradistinguishing them from 

 the fhocidir, in none of the species of which is the angle of the jaw 

 so produced. The Thulacotherium differs from the genus Didelphyt in 

 the greater number of it* molars, and from every ferine quadruped 

 known at the time when Cuvier formed his opinion respecting the 

 nature of the fossil. This difference in the number of the molar 

 teeth, which Cuvier urged as evidence of the generic distinction of 

 the Ktonesfield mammifernus fossils, has since been regarded as one 

 of the proofs of their Saurian nature ; but the exceptions by excess 

 to the number seven, assigned by M. Do Bloinville to the molar teeth 

 in each ramus of the lower jaw of the insectivorous Mammalia, are 

 well established, and have been long known. The insectivorous 

 C'ArjwocUore, in the order Perec, has eight molars in each ramus of the 

 lower jaw ; the insectivorous ArmaMloi have not fewer j and in one 

 sub-genus (Priodon) there are more than twenty molar teeth on each 

 aide of the lower jaw. The dental formula! of the carnivorous 

 Cttacta, again, demonstrate the fallacy of the argument against the 

 mammiferous character of the Thylacothtrium founded upon the 

 number of iU molar teeth. From the occurrence of the above 

 exceptions in recent placeutal Mammalia, the example of a like excess 

 in the number of molar teeth in the marsupial fossil ought rather to 

 have led to the expectation of the discovery of a similar case among 

 existing Marsupial*, and such an addition to our zoological catalogues 

 has, in fact, been recently made. In the Australian quadruped 

 described by Mr. Waterhouse under the name of Mynnecoliui an 

 approximation towards the dentition of the T/iylatolherium is exempli- 

 fied, not only in the number of the molar teeth, which is nine on each 

 tide of the lower jaw in the Myrmecobitu, but also in their relative 

 i*, structure, and disposition. Lastly, with respect to the dentition, 

 Professor Owen says it must be obvious to all who inspect the fossil 

 and compare it with the jaw of a small DidtlfJiyt, that, contrary to 

 wrtion of M. De BUinville, the teeth and their fang* are 



the 



arranged with as much regularity in the one as in the other, and that 

 no argument of the Saurian nature of the fossil can be founded on 

 this part of its structure. 



With respect to M. De Blainvillo's assertion that the jaw is compound, 

 Professor Owen stated that the indication of this structure near the 

 lower margin of the jaw of the Thylacothmum is not a true suture, 

 but a vascular groove similar to that which characterises the lower 

 jaw of Diddphyt, Opouum, and tonic of the larger species of Sorex. 

 (' Geol. Prof.') 



Jaw of nylacothrrivm Prerottii. Upper figure magnified. 



Some discussion having ensued, in which Dr. Grant and Sir. Ogilby 

 expressed opinions in support of M. De Blainville's views, Professor 

 Owen, on the occasion of reading, on the 9th of December following, his 

 paper on PhatcoloOirrium, being the second part of the ' Description 

 of the Remains of Marsupial Mammalia from the Stonesfield Slate,' 

 gave a brief nummary of the characters of the T/iylacothfrium, 

 described in the first part of the memoir, and which he conceived 

 fully proved the mammiferous nature of that fossil. He stated that 

 the remains of the split condyles in the specimen demonstrate their 

 original convex form, which is diametrically opposite to that which 

 characterises the same part in all reptiles and all ovipara ; that the 

 size, figure, and position of the coronoid process are such as were never 

 yet witnessed in any except a zoophagous mammal endowed with a 

 temporal muscle sufficiently developed to demand go extensive an 

 attachment for working a powerful carnivorous jaw ; that the teeth, 

 composed of dense ivory with crowns covered with a thick coat of 

 enamel, are everywhere distinct from the substance of the jaw, but 

 have two fangs deeply imbedded in it ; that these teeth, which belong 

 to the molar series, are of two kinds ; the hinder being bristled with 

 five cusps, four of which are placed in pairs transversely across the 

 crown of the teeth, and the anterior or false molars, having a different 

 form, and only two or three cusps characters never yet found united 

 in the teeth of any other than a zoophagous mammiferous quadruped ; 

 that the general form of .the jaw corresponds with the preceding more 

 essential indications of its mammiferous nature. Fully impressed with 

 the value of these characters, as determining tho class to which the 

 fossils belonged, Professor Owen stated that he hsd sought in the next 

 place for secondary diameters which might reveal the group of Mam- 

 malia to which the remains could be assigned, and that he had found 

 in the modification of the angle of the jaw, combined with the form, 

 structure, and proportions of the teeth, sufficient evidence to induce 

 him to believe that the Thylacotheriwn was a marsupial quadruped. 



Professor Owen then recapitulated the objections against the mam- 

 miferous nature of the Thylocotherian jaws from their supposed 

 imperfect state, and repeated his former assertion that they are in a 

 condition to enable these characters to be fully ascertained : he next 

 reviewed, first, the differences of opinion with respect to the actual 

 structure of tho jaw ; and, secondly, with respect to the interpretation 

 of admitted appearances. 



1. As respects the structure. It has been asserted that the jaws 

 must belong to cold-blooded Ycrtebratn, because the articular surface 

 is in the form of an entering angle : to which Professor Owen replied 

 that the articular surface is supported on a convex condyle, which is 

 met with in no other class of Vertcbra'.a except in the Mammalia. 

 Again, it is asserted that the .teeth are all of an uniform structure, as 

 in certain reptiles ; but, on reference to the fossils, Professor Owen 

 stated that it will be found that such is not the case, and that the 

 actual difference in tho structure of the teeth strongly supports the 

 mammiferous theory of the fossils. 



2. With respect to the argument founded on an interpretation of 

 structure, which really exists, the author showed that the Tliylato- 

 t/icrium having 1 1 molars on each side of the lower jaw is no objection 

 to its mammiferous nature, because among the placenta! Carnirora 

 the C'anit Meyaloti* has constantly one more grinder on each side of 

 the lower jaw than the usual number ; because the Chrytochlore, among 

 tho JnKcdvora, lm also 8 instead of 7 molars in each ramus of the 

 lower jaw ; and the Myrmccoliiiu, among the Manujiiala, has 9 molars 

 on each side of the lower jaw ; and because some of the insectivorous 

 ArmadHJoi and zoophagous Cetacca offer still more numerous and 

 reptile-like teeth, with all the tnie and essential characters of the 

 mammiferous class. The objection to the false molars having two 

 fangs, Professor Owen cbowed was futile, as the greater number of the 



