4^ 

 188».] -tu'j [Cope. 



glenoid, and generally looking more downwards than outwards. I call this 

 the sub squamosal. These foramina may he arranged in four sets, as follows : 



I. Looking downwards ; 

 Postglenoid. 

 Subsquamosal. 

 II. Looking outwards ; 

 Pditsquamosal. 

 Posiparietal. 



III. Looking upwards ; 



Supraglenoid. 



IV. Looking backwards ; 



Mastoid. 



Some foramina of the same region are not necessarily connected with 

 the sinus lateralis. Hyrtl, 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 diplo'etica," which is formed by the 

 junction of the occipital branch of the carotid with an ascending branch of 

 the temporo-maxillaris division of the carotid. The a. diplo'etica issues in 

 a foramen which perforates the parietal bone on the orbital border. These 

 two foramina may be called the/, diploeticum posterior and/, d. anterior, 

 respectively. The former enters from the fundus of the same small fossa, 

 which is also perforated in its superior portion by the /. postsquamosale, 

 the canal from the latter foramen taking the usual vertical direction. 



Still another foramen exists, 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 Marsupialia it enters a fossa of the 

 squamosal bone, which may or may not he partially filled with cancellous 

 tissue. I call this the foramen postsygomaticum. 



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, f 



Monotremata. 



Tachyglossus. The only foramina are the//, diplo'etica anterior nnd pos- 

 terior, and the postsygomaticum. The anterior half of the canal connect- 

 ing the former two has no external wall. 



Ornithorhynelius. Postzygomatlc large and passing through the zygo- 

 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 



* Denkschriften Wiener Akademie, 1854, T. Ill, pi. 1. 



fMost of these are preserved in my private collection ; for a few I am indebted 

 to the Museum of the Philadelphia Academy. 



