127 



most developed in the skull of the Myrmecohius fasciatus, where the 

 orbit is large ; hut the bon)f boundcary of the orbit is not complete 

 in any of the Marsupials. In the Myrmecohius there is a deep notch 

 at the middle of the supra-orbital ridge. I have found the frontal 

 suture obliterated only in the Virginian Opossum and Petaurists ; 

 but in the latter it is remarkable, that the other sutures of the head, 

 as the lambdoidal and sagittal, continue distinct. 



" The frontal bones are chiefly remarkable for their anterior expan- 

 sion, and the great share which they take in the formation of the na- 

 sal cavity. In the Thylacine the part of the cranium occupied by the 

 frontal sinuses exceeds in breadth the cerebral cavity, from which it 

 is divided by a constriction. 



" The lachrymal bones vary in their relative size in ditFerent Mar- 

 supiata. In the Koala they extend upon the face about a line be- 

 yond the anterior boundary of the orbit ; and at this part they pre- 

 sent a groove with one large, and two or three small perforations ; 

 in the Wombat their extent upon the face is slightly increased ; it 

 is proportionally greater in the Kangaroos, Potoroos, Phalangers, 

 and Dasyures, in which this part of the lachrymal bone presents two 

 perforations, but it is close to the orbit. The Thylacine, as compared 

 with the Wolf, presents a greater extent of the facial portion of the 

 lachrymal bone, and thus indicates its inferior type. In the Myr- 

 mecohius the lachrymal bone exhibits its greatest relative develop- 

 ment. 



" The malar bone is very strong and of great extent in all the 

 Marsupiata : least developed in the Perameles lagotis, it here presents 

 a singular form, being bifurcate at both extremities ; the processus 

 zygomuticus mnxillce svperioris is wedged into the cleft of the ante- 

 rior fork ; the corresponding process of the temporal bone fills up 

 the posterior space ; the lower division of this bifurcation is the 

 longest, and in all the Marsupiata enters into the composition of the 

 articular surface for the lower jaw, except in the Petaurists, where 

 it just falls short of this part. The anterior bifurcation of the malar 

 bone is not present in the Marsupiata generally : the external malo- 

 maxillary suture forms an oblique and almost straight line in the 

 Wombat, Phalanger, Opossum, Dasyurus, and Kangaroo. Owing 

 to the low development of the zygomatic process of the superior 

 maxillary in the Wombat, the malar bone is not suspended in the 

 zygomatic arch in this Marsupial, as in the placental Rodentia. It 

 is of relatively much larger size, and of a prismatic form, arising 

 from the development of the obhque external ridge above described. 

 In the Kangaroo, Potoroo, Great Petaurus, and Phalanger, it is tra- 

 versed externally by a ridge showing the extent of attachment of 

 the masseter ; in the Koala the ridge extends along the bone near 

 the upper margin, and the surface below presents a well-marked ex- 

 cavation. 



" The nasal bones vary in their form and relative size in the dif- 

 ferent genera ; they are longest and narrowest in the Perameles, 

 shortest and broadest in the Koala. Their most characteristic 

 structure is the expansion of the upper and posterior extremity, 



