20 PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



spicuous ; it is much more prominent on the sixth and still more on the 

 seventh. The transverse processes are much less extended antero-pos- 

 teriorly than on the preceding vertebrae, but appear to be wider transversely. 



As already pointed out, the neck as a whole is short, which is also true 

 of all of the known Santa Cruz representatives of the family. Taking the 

 basal length of the skull as loo, that of the neck is 72.2, as nearly as can 

 be calculated from the material now available. 



The number of trunk vertebras (PI. I) is not definitely known, but it is 

 highly probable that this number was 21 or 22. Of these 15 were prob- 

 ably thoracic, and it is certain that there cannot have been less than 6 

 lumbars. Assuming that there were fifteen thoracic vertebrse, their com- 

 bined length, measured around the ventral curve of the spinal column, may 

 be calculated as approximately 136, the basal length of the skull being 100. 



The first thoracic vertebra has a broad, much depressed centrum, with 

 well defined ventral keel ; the prezygapophyses are of the cervical type, 

 while the postzygapophyses have the thoracic pattern and are placed on 

 the ventral side of the neural arch ; the neural spine is not very high and 

 is quite slender, with a moderate inclination backward ; the transverse 

 processes are heavy and prominent and bear large facets for the ribs. After 

 an interval of perhaps four vertebrae, not represented in the collections, 

 follows a series of four in their natural connection. These have rather 

 small, slightly depressed and somewhat opisthocoelous centra, of the ordi- 

 nary ungulate type, and slender neural spines which are strongly inclined 

 posteriorly. In the figure of the skeleton (PI. I) this inclination does not 

 appear so marked, because of the oblique position of the centra in this 

 part of the column. The transverse processes are quite prominent and 

 arise high up on the sides of the neural arch. 



In the posterior part of the thoracic region the centra are larger than in 

 the median portion and quite broad and depressed ; the zygapophyses 

 are cylindrical and interlocking, very much like those typical of the Artio- 

 dactyla, and the metapophyses are very prominent. The short transverse 

 processes still arise from the neural arches rather than from the centra ; 

 even on the last thoracic these processes have facets for the rib-tubercles. 

 The neural spines, which are rather low, are thin transversely, plate-like and 

 broad antero-posteriorly. The penultimate thoracic is the anticlinal verte- 

 bra, the neural spine of the last one having a distinct forward inclination. 



The lumbar formula in Diadiaphorus is 6-7 though not more than six 



