MAY, 1921. AMERICAN MARSUPIAL, C^NOLESTES OSGOOD. 81 



branch of the transverse process is only slightly developed. The superior 

 branch of the transverse process is directed obliquely backward and 

 upward and at its base is pierced by the arterial canal. In the fifth it is 

 slightly thicker than in the third and fourth, has less backward deflection 

 and is definitely faceted at the tip. 



The sixth cervical is similar in general features to that in the majority 

 of marsupials. The arterial canal perforates the base of the transverse 

 process as usual but it is to be noted that the dorsal wall of the canal is 

 very much thicker than the ventral. The inferior branch of the trans- 

 verse process is expanded into a dolabriform plate practically parallel 

 with the spinal axis. This has only very slight forward projection but is 

 extended caudad nearly or quite to the plane of the centrum of the 

 first thoracic vertebra. 



The seventh cervical has a slightly higher spinous process than the 

 three preceding vertebrae, but the distinction is not marked. It has the 

 superior branch (diapophysis) of the transverse process with its tubercle 

 directed almost at right angles to the spinal axis in the horizontal plane 

 of the body of the vertebra. The inferior branch (parapophysis) and 

 consequently the arterial canal are obsolescent, that is, they are variable, 

 being present in some specimens and reduced or absent in others. In 

 one specimen, the arterial canal on the left side of the vertebra is 

 enclosed by the merest bony thread representing the parapophysis and 

 having no tubercle. On the right side of the same vertebra, the condi- 

 tion is similar but the canal is exceedingly small, scarcely one-tenth as 

 large as that on the left side. In several other specimens, the seventh 

 cervical is quite imperforate, the vertebral side of the base of the trans- 

 verse process being merely grooved (PL XI, figs. 4-6). In a single 

 specimen of Phascologale, the lower boundary of the arterial canal is 

 incomplete, indicating a condition very similar to that in Canolestes; in 

 a single specimen of Sarcophilus, one side is perforate and the other 

 imperforate. The seventh cervical is imperforate in Trichosurus, 

 Dasyurus, Perameles, Sarcophilus, Didelphis, Marmosa, and Peramys. 

 The arterial canal has complete bony boundaries in Thylacinus, Petaurus, 

 Philander, Phascolomys, Phascolarctos, and the Macropodidae. It is 

 complete also in the extinct genera Borhyaena and Cladosictis. Thus 

 in the majority of diprotodonts the seventh cervical is perforated and 

 in the majority of polyprotodonts it is imperforate, although the 

 perforate condition is more primitive. In this as in other respects, 

 therefore, C&nolestes combines the characters of the two groups. 



None of the cervicals have foramina piercing the lateral wlls of the 

 neural arches like those in some other marsupials (Thylacinus, Dasyurus, 

 Didelphis, etc.). 



