52 Mammalia. Marsupialia. 



tremity. In the stronger carnivorous Marsupials the exterior of 

 the cranium is characterised by bony ridges and muscular impres- 

 sions, varying directly with the development of the temporal 

 muscles, the extreme development being found in the Yirginian 

 Opossum, in which the sides of the cranium meet above at an acute 

 angle, and send upward from the line of their union a remarkable 

 elevated sagittal crest, which, in mature skulls, is proportionally 

 more developed than in any of the Placental Sectoiialia. In the 

 smaller Herbivorous and Insectivorous species the cranium presents 

 a convex surface, as in birds. 



The Occipital region, which is generally plain, and vertical in po- 

 sition, forms a right angle with the upper surface of the skull, from 

 which it is separated by an occipital, or lamboidal crista. The ele- 

 ments of the occipital neural arch remain longer distinct in Marsu- 

 pials than in most other Mammals. The Condyles are each perforated 

 anteriorly by two foramina in most of the Marsupialia. The Fora- 

 men magnum is of great size in relation to the capacity of the cranium. 

 The Sagittal suture^ between the Parietals, is obliterated in those 

 species in which a bony crista is developed, as also in some aged 

 animals. An Interparietal hone is generally present. The Coronal 

 suture presents, in most of the Marsupialia, an irregular angular 

 course, forming a notch in the frontals on each side, and receiving 

 a corresponding triangular process of each frontal bone. The Frontals 

 are chiefly remarkable for their anterior expansion and the great 

 share which they take in the formation of the nasal cavity. The 

 JExtraorhital foramen is a good Marsupial character. The most 

 characteristic structui'e of the JVasal bones is the expansion of their 

 upper and posterior extremity. The Prcemaxillaries always contain 

 teeth, and the ratio of the development of these bones con'csponds 

 with the bulk of the dental apparatus which they support, they are 

 consequently largest in the Wombat. The Alalars are generally very 

 strong, and of great extent. The Zygomatic arches are always com- 

 plete, and usually strongly developed, but do not vary in size as 

 directly with the diet as in preceding orders. Most Marsupials 

 have a Sphenoidal hdla, foimcd by the expansion of the base of the 

 Sphenoid ; Acrobates and Perameles lagotis have a second bulla 

 formed by the expansion of the Petrous bone ; the Petrous lone is 

 generally of small size, and limited to the office of protecting the 

 parts of the internal ear ; the Glenoid cavity presents a character- 

 istic structure in most of the Marsupials in not being exclusively 



