Mackintosh — Premaxillo-Frontal Suture in Skull of Koala. 335 



LIV. ]^OTE OK THE OCCTJEEENCE OF A PEHilAXILLO-FEONTAL SuTXTRE 



IN THE Skull of the Koala (Phascolaectos cineeeus). By 

 H. W. Mackintosh, Professor of Zoology, Trinity College, Dublin. 

 (With Plates X. to XIII.) 



[Read, jSTovember 29, 1879.] 



In the collection of the Museum of Anatomy and Zoology of the Univer- 

 sity there is a skeleton of the marsupial Koala (Phascolarctos cinereus, 

 Fischer), the skull of which, while normal in other respects, exhibits 

 a distinct contact between premaxillse and frontals, an arrangement 

 which, so far as I can ascertain, has not yet been described. The 

 animal to which the skeleton belonged had been obtained some years 

 ago by Professor Macalister (to whose courtesy I owe the present 

 opportunity of describing the skull), who published an account of its 

 anatomy in the Annals and Magazine of Natural History for 1872, 

 Yol. X. p. 127. 



In the Museum of the Royal Dublin Society there is another 

 skeleton of Koala, the skull of which Dr. Carte, the Director of the 

 Museum, has kindly allowed me to examine; and in it I find also a 

 premaxillo-frontal suture, but it is apparent only on the right side, 

 where it is very small, being less extensive than that on the left side 

 in the specimen here figured. In their general features they both agree 

 with the descriptions given in manuals and memoirs, and on com- 

 paring them with the drawing published by Owen,^ I find that the 

 resemblance is sufiiciently close in other respects. 



In its cranial osteology the genus Phascolarctos departs, as is well 

 known, from many of the characters of the Didelphs, and suggests 

 sundry resemblances to Monodelphian skulls. Thus, for instance, the 

 zygomatic arches are very long, and run parallel to the axis of the 

 cranium, as in no other living marsupial, and only to a comparatively 

 slight degree in the fossil Xototherium. Then we notice the large 

 tympanic bullae (which have been compared to those in the pig), the 

 abruptly truncated nasal aperture, the rounded premaxillae, the 

 prominent paroccipital processes, and the vertical supra-occipital, all 

 rodent characters, and each of which connects the Koala with some 

 other marsupial genus, as I shall presently point out. 



On examining the anterior part of the skull (Plate X., fig. 1), it 

 will be seen that the ascending process of the maxilla (7), which, in all 

 the other marsupials which I have examined, comes into contact with 

 the nasal (8) of its own side, and interposes between the premaxilla (9) 

 and frontal (4), is here shorter than usual, and thus these two bones 

 come into contact slightly, but distinctly, on the right side, and to a 

 much more marked degree on the left. In a skull of the same animal, 



" On the Fossil Mammals of Australia," Fhil. Trans., toI. clxii. part 1. 



