66 



markable repetition, in a dorsal vertebra, of a structure characteristic of the cer- 

 vical vertebrse, appears to be peculiar to the Mylodon amongst Mammalia. It is 

 present in the posterior dorsal vertebr3e of birds, one or more of which are occa- 

 sionally, with their costal appendages, anchylosed to increase the anterior extent 

 of the sacrum in that class. The complicated articular processes in front of the 

 last dorsal vertebra indicate that it was interlocked with a double articular process 

 on each side of the posterior part of the preceding dorsal vertebra. The superior 

 pair of these posterior articular processes of the fifteenth dorsal, which are broken 

 off in the specimen, were received into longitudinal concavities (r) , between the 

 upper anterior articular processes and the commencement of the spinous process ; 

 the lower and outer posterior processes of the fifteenth dorsal were received into 

 the concavities between the upper and middle anterior articular processes of the 

 anchylosed dorsal ; the third and lowest articular process of this vertebra was 

 adapted to a cavity at the posterior part of the neural arch of the fifteenth dorsal. 

 Part of the interspace between the upper and middle articular process appears to 

 have been occupied by the vessel or nerve which traversed the base of the trans- 

 verse process. The interspace between the middle and lower articular process forms 

 part of the conjugational hole for the transmission of the fifteenth dorsal nerve. 

 A plate of bone is continued backwards from the base of the transverse pro- 

 cess of the last dorsal to that of the first lumbar vertebra. In this vertebra the 

 transverse process assumes the form of a broad plate (c) with a convex external 

 margin, directed obliquely upwards and outwards. Nearly the whole of the 

 posterior margin of this transverse plate is continuous with the corresponding 

 plate of the second lumbar vertebra {d), the outer extremity of which is joined by 

 continuous ossification to the corresponding process of the third lumbar, and 

 with it to the upper and posterior part of the iliac labium ; the corresponding 

 processes of the first and second sacral vertebrae are joined by a similar conti- 

 nuity of ossification with the ilium, and progressively increase in thickness. 

 The transverse processes of the third, fourth, and fifth sacral vertebrae form the 

 inner and upper boundaries of the sacro-ischiadic foramina (e), and terminate in 

 a ridge (i) which is bent upwards and outwards. The transverse processes of 

 the sixth and seventh vertebrae extend outwards and downwards, slightly expand 

 as they become confluent with the tuberosities of the ischia (/), and thus com- 

 plete the osseous boundary of the sacro-ischiadic foramina. 



