8o FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XIV. 



divided into two parts one of which probably appertains to the odontoid 

 and the other is the usual hypapophysis of the axis. The anterior of 

 these is a sharp hooked process rising from the base of the odontoid and 

 projecting backward along the median line. The posterior process is a 

 ridge rising beneath this hook and gradually becoming more elevated to 

 terminate in a tubercle which has slight projection caudad beyond the 

 centrum and thus to some extent effects imbrication with the front 

 edge of the body of the third vertebra. InMarmosa there is a prominent 

 axial hypapophysis and in the skeleton of a half -grown Didelpkis with 

 the odontoid still distinct there is a small median knob but in adults I 

 find nothing in any marsupial comparable to the hooked process 

 described above. It very strongly suggests the large recurved hypapo- 

 physes of Ornithorhynchus. The posterior border of the neural arch in 

 lateral view presents an even curve from the spine to a prominent angle 

 above the postzygapophysis. The neural canal has the outline of a 

 horseshoe and its width and depth are nearly equal. 



The transverse process of the axis has a superior and an inferior 

 division, each a small backwardly directed projection from the caudal 

 aspect of the pedicel of the arch, ventrad of the postzygapophysis and 

 caudad of the prezygapophysis. The extremities of these processes are 

 articulated to the slightly produced basal angles of a small, distinct, 

 subtriangular pleurapophysis or cervical rib which serves to complete 

 the boundary of the arterial canal and which is obviously the homologue 

 of the fully ankylosed processes serving the same purpose in the suc- 

 ceeding vertebrae. In a fully adult animal this cervical rib has only 

 cartilaginous union with the vertebra and in the undesiccated specimen 

 it is freely movable (PI. XI, fig. 7). It is essentially similar to the 

 persistently distinct cervical ribs in Ornithorhynchus and in reptiles. 

 It has not been reported among marsupials or higher groups except in 

 Perameles and Phascologale. In Perameles lagotis, it is noted by Owen 

 (Trans. Zool. Soc. Lond., II, p. 394, 1841) in a single instance. The only 

 skeleton of Perameles (P. nasuta) I have been able to examine, has the 

 axial pleurapophysis fully ankylosed. Whether it is normally so in this 

 genus, therefore, is uncertain; but its persistence as a distinct part in 

 C&nolestes is none the less significant. Beddard (1902, p. 119) mentions 

 a separate axial rib for Phascologale. 



The third, fourth and fifth cervicals are not peculiar and resemble 

 each other in general characters. In the third the neural canal is rela- 

 tively deeper, its vertical and transverse diameters being nearly equal, 

 whereas in the fourth and fifth the width considerably exceeds the 

 depth. In the third the spinous process is very slight; in the fourth and 

 fifth it is a low but distinct mammillate process. In all three the inferior 



