26 PATAGONIAN EXPEDITIONS! PALAEONTOLOGY. 



each succeeding vertebra and are most conspicuous on the last one. Curi- 

 ously enough, these grooves are asymmetrical, being longer and deeper 

 on the right side than on the left. 



The lumbars are four in number and this, with eleven thoracics, would 

 give a total of fifteen trunk-vertebrae, the formula common in Tafit, though 

 in that genus the number varies from thirteen to sixteen. The lumbar 

 centra are of moderate size, not greatly exceeding those of the posterior 

 thoracic region, nor do they increase much in size backward, though that 

 of the third is somewhat larger that the others ; they are short, broad and 

 depressed and the second has on the ventral side a pair of short, parallel 

 ridges, which are repeated, though very obscurely, on the third and fourth ; 

 all the centra, except the fourth, have grooves like those of the last four 

 thoracics, which are best shown on the first. The neural spines are some- 

 what longer and broader than those of the hindermost thoracic region and 

 are recurved rather than inclined ; the free end of each spine is thickened 

 and cleft behind to receive the anterior edge of the succeeding spine ; the 

 metapophyses are exceedingly prominent and reach their maximum size 

 on the third vertebra. Each of the lumbars has three pairs of articular 

 processes in front and behind. 



The sacrum is much like that of Tatu, being very long and composed 

 of nine vertebrae intimately fused together. As a whole and seen from 

 the dorsal side, the sacrum is broad in front, narrows gradually to the end 

 of its contact with the ilium and then again expands, but more suddenly, 

 and attains its greatest breadth at the hinder end. Ventrally, the sacrum 

 is very narrow in front, broadening posteriorly. These alternate con- 

 tractions and expansions affect chiefly the transverse processes, the centra 

 narrowing regularly from the first to the last, though in the middle region 

 they become extremely thin and plate-like. The neural spines form a low 

 continuous ridge and the neural canal is small. The first sacral vertebra 

 has very prominent metapophyses and two pairs of prezygapophyses, like 

 those of the lumbars, but on the other vertebras, except the eighth and 

 ninth, the zygapophyses have entirely disappeared. Vertebrae one to three 

 are connected with the ilia, ventrally by pleurapophyses and dorsally by 

 the transverse processes, while the fourth reaches the ilia only by means 

 of the latter. Next follow two vertebrae which are not in contact with the 

 pelvis at all, succeeded by three which unite with the ischia by their 

 greatly developed transverse processes. 



