PIGMY FLYING-OPOSSUM. 
341 
The following are the admeasurements of a skull of 
Acrobata 
pygmiea in the British Museum :— 
/ 
Inches. 
Lines. 
Length of skull ... . 
n 
Width of ditto 
6* 
Total length of palate 
5 
From front of foremost incisor to back of last 
molar ... ... ... ... . 
Length of nasal bones . 
Width of interorbital space ... . 
Length of lower jaw . 
5! 
Height of ditto in a vertical line dropped from 
the apex of the coronoid process . 
2} 
The bones of the skull of Petauriis jtygmcms, like those 
of the little Phalangers formiug the section Dromicia, are 
extremely thin and semi-transparent; the cerebral portion of 
the cranium is large in proportion to the facial part; the 
occipital opening is very large, and the zygomatic arelies are 
slender: the angular portion of the lower jaw is in the form 
of a slender pointed process, directed inwards and backwards 
so as to form an obtuse angle with the plane of the horizontal 
ramus: the coronoid process is also slender. 
As compared with the skull of a species of Dromicia now 
before me (the D. Neillii), that of P. pijgmmis differs in 
certain points which are worthy of notice. In the Dromicia the 
posterior root of the zygoma is much expanded, or, as it were, 
inflated, to increase the air-cells of the auditory chamber, 
whilst in the Acrobata there is no such expansion of the 
zygomatic process of the temporal bone. The auditory bulla 
is much more prominent in the Dromicia than in the small 
Flying-Phalanger, and is almost entirely formed by an ex¬ 
pansion of the petrous element of the temporal bone; in 
Petaurus pyy miens the auditory bulla is formed partly by the 
same portion of the temporal bone, but chiefly by the great 
ala of the sphenoid. 
