9 
_ 
Some foramina of the same region are not necessarily connected with 
the sinus lateralis. Wyrtl, in his essay* on the arterial system of the 
Edentata, shows that a foramen near to the postsquamosal of the Tamandua 
tetradactyla, gives passage to an ‘‘arteria diploética,’’ which is formed by the 
junction of the occipital branch of the carotid with an ascending branch of 
the temporo-mawillaris division of the carotid. The a. diploética issues in 
a foramen which perforates the parietal bone on the orbital border. These 
two foramina may be called the f. diploéticum posterior and f. d. anterior, 
respectively. The former ‘enters from the fundus of the same small fossa, 
which is also perforated in its superior portion by the f. postsquamosute, 
the canal from the latter foramen taking the usual vertical direction. 
Still another foramen ex'sts, which is, so far as my present knowledge 
goes, confined to the Monotremata and Marsupialia. It enters the posteri- 
or base of the zygomatic portion of the squamosal, and is directed forwards. 
In Tachyglossus it passes through the base of the zygoma, issuing in the 
base of the zygomatic fossa. In the Marsupiulia it enters a fossa of the 
squamosal bone, which may or may not be partially filled with cancellous 
tissue. I call this the foramen postzeygomaticum. 
I now give the results of my observations on the crania of the most im- 
portant genera which I -have observed, one hundred and sixteen in number.+ 
MoNoOTREMATA. 
‘ 
Tachyglossus. The only foramina are the f.f. diploética anterior and pos- 
terion, and the posteygomaticum. The anterior half of the canal connect- 
ing the former two has no external wall. 
Ornithorhynchus. Postzygomatic large and passing through the ZY g0- 
ma; postsquamosal large ; no other foramina. 
MARSUPIALIA. 
The types of this order generally have the postglenoid, and hardly ever 
have the supraglenoid or postparietal. They are generally distinguished 
by the presence of the subsquaniosal, but in Hypsiprymnus and Macropus 
this foramen becomes the postsquamosal, through the failure of the post- 
zygomatic crest. It need not be confounded with another foramen also 
found in these genera, which enters above the meatus auditorius externus, 
and communicates with the tympanic chamber, and which I call the su- 
pratympanic foramen. The subsquamosal enters the sinous canal, and in 
Phascolarctos, where the postglenvid is wanting, constitutes its only exter- 
nal outlet. The order is further characterized by the presence of the post- 
zygomatic foramen. 
Phascolomys ; postzygomatic chamber enormous, extending above mea- 
* Denkschriften Wiener Akademie, 1854, T. ILI, pl. 1. 
t+ Most of these are preserved in my private collection ; for afew Iam indebted 
to the Museuin of the Philadelphia Academy. 
