PEOPESSOE OWEN ON MACEOPUS. 423 



The malar contributes the outer half of the floor of the orbit, articulating there with 

 the laciymal and maxillary ; the zygomatic part of the malar (ib. fig. 1, 26) is deep or 

 vertically extended ; it articulates by an oblique suture with the maxillary pier of the 

 arch (21 X ), and diverges to receive, by a large and deep notch, the pointed fore part of 

 the squamosal zygoma (27). The malar is excavated, as it were, below the orbital rim, 

 from which a ridge extends backward nearly parallel with the horizontal part of the 

 malo-squamosal suture ; the hind end of the malar expands horizontally or is produced 

 inward to form the fore part of the glenoid cavity (ib. fig. 3, 26x) or mandibular arti- 

 culation. The zygomatic part of the squamosal (27') rather exceeds in depth that of 

 the malar, rising abruptly behind from its attachment to the cranial part (27'). Close 

 to this attachment is the squamosal venous foramen (m) ; below this is a larger vacuity 

 (tympano-zygomatic cell, n) between the squamosal and tympanic ; and behind this is 

 the shallower " tympano-squamosal " cell. The cranial plate of the squamosal ( 27' ) 

 unites with the parietal and alisphenoid, with the superoccipital and mastoid, and with 

 the tympanic. 



The tympanic (PI. LXXIV. fig. 1, 28) is a cylinder, expanding toward the brain-case into 

 an irregular triedral bone. The upper and fore side receives the postglenoid process ; 

 the under and outer part (ib. fig. 1, 28) articulates with the alisphenoid (e), the inner 

 part with the petrosal (ib. fig. 3, le), the hinder part with the mastoid ( 8 ). The tym- 

 panic long retains its individuality. The auditory canal is directed outward and a 

 little upward and backward; its outlet is circular; but the canal loses vertical and 

 gains transverse extent as it passes inward, and the greater extension of its lower wall 

 gives an oblique position to the inner end supporting the " membrana tympani." 



The pterygoid (ib. fig. 3, 24) has an antero-posteriorly extended base, which arti- 

 culates with the basi- and alisphenoids, completing externally or extending below the 

 large concavity of the pterygoid process of the alisphenoid, and extending internally 

 the hinder aperture of the nasal passage. The lower end of the pterygoid articulates 

 with the inner side of the pterygoid process of the palatine ( 20" ), and develops a short 

 compressed "hamular" process ( 24') slightly bent outward. 



The petrosal (ib. fig. 3, 10)^ has two free surfaces — the "cranial" and "basilar." 

 The former is the most extensive, is bifurcate anteriorly and impressed near its hind 

 part by a deep cerebellar pit, below and a little in advance of which is the " meatus 

 auditorius intemus ;" a sharp ridge overhangs the cerebellar or appendicular pit^. The 

 exposed basilar surface is small and narrow, pointed anteriorly, grooved externally 

 for a venous canal, and, in most Kangaroos, crossed by a slender bar of the exoccipital 



' I have failed to appreciate the gain to anatomy by the change of this name to "periotic;" the petrosal 

 Burrounds only one part of the " organ of hearing " in the Tbylacine as in other Mammals. The mastoid is 

 developed from a separate ossific centre in all Vertebrates, and remains distinct from the petrosal in most 

 Haematocrya. 



' The cerebellar appendage which occupies this pit is not the homologue of the " flocculus " of E«il, 



