224 Bulletin American Museum of Natural History. [Vol. XX^"II, 



Postglenoid. This venous foramen, which is only exceptionally absent 

 in mammals occurs also in the Marsupials. 



Postziigomatic. This small venous foramen, first described by Cope 

 (1880), is associated with the postglenoid, and like it contributes to the 

 system which comprises the transverse occipital sinus, the mastoid, post- 

 parietal, the jugular (for. lac. post.) and other foramina. It opens below or 

 within the lip of the postglenoid foramen and runs forward. i\.s observed 

 by Cope (1880, p. 454) it is characteristic of the Marsupialia and distin- 

 guishes the carnivorous Marsupials from their Placental analogues. 



Subsquamosal (Cope). This is another tributary to the transverse canal. 

 In the Polyprotodonts it is located in the external portion of the roof of 

 the auricular meatus, behind and above the postglenoid + post zygomatic 

 opening, and below the squamosal ridge which connects the zygoma with 

 the lambdoidal crest. In the Diprotodonts through the failure of the post- 

 zygomatic ridge the subsquamosal sometimes becomes identical with the 

 post squamosal (Cope). 



Postsquamosal (Cope). This is another part of the venous system of the 

 transverse sinus. It is a lateral foramen in the postero-superior part of the 

 squamosal in front of the lambdoidal crest and above and behind the sub- 

 squamosal foramen. It is often reduced or absent. 



Mastoid foramen. On the occipital surface of the mastoid bone at or 

 near its supero-external corner. A part of the same venous system. Fre- 

 quently, but not always present in JNIarsupials and primitive Placentals. 



Jugular foramen ("For. lac. post.," "for. vagi"). The final member of 

 the venous system under consideration. Also transmits nerves IX, X, 

 XI. In Didelphis and TJu/larijnus it lies immediately postero-externally 

 to the posterior carotid foramen, posterior to the petrosal and internal to the 

 base of the jiaroccipital process (Fig. 1, A, /. /. p.). 



Stijlomastoid foramen and canal. At the postero-external angle of the 

 petrosal is the stylomastoid foramen, which transmits the facial or seventh 

 nerve, after its passage through the petrosal (p. 430). The stylomastoid 

 foramen is constant in mammals, but by the growth of the surrounding parts 

 it is often covered up or difficult to locate. In Didelphis it is exposed in 

 front of the internal base of the mastoid. In Thylacyiius it lits at the bot- 

 tom of a canal formed by the tympanic, the mastoid and the paroccipital. 

 In Diprotodonts the canal appears to issue on the postero-external border of 

 the skull between the tympanic and the mastoid. The stylohyoid bone is 

 attached to the petrosal in or near the stylomastoid canal, often postero- 

 internally to it. 



Condijlar foramen. Located immediately in front of the occipital condyle 

 and transmitting the twelfth or hypoglossal nerve. 



