226 PROF. H. Gr. SEELET ON A.RISTOSUCHUS PUSILLUS. 



sacrum and that of most other British Wealden reptiles ; for while 

 the transverse processes or sacral ribs in Iguanodon, Uylceosaurus, 

 Megalosaurus, &c. are given off at the junction of the centrums, the 

 transverse processes are here, as Sir IL Owen's figure shows, given 

 off from the individual vertebrae to which they belong (fig. 14), as 

 in the American genera described by Marsh, such as Morosaurus, 

 Apatosaurus, Atlantosaurus, Stegcsaurus, Brontosaurus, &c, and as 

 in Omosaurus. 



The five sacral vertebrae measure 12 centimetres. The first two 

 (fig. 14, i, 2) are very slightly longer than the succeeding three. The 

 bodies of the vertebrae are constricted from side to side, so that though 

 the flat transversely ovate articular face of the first vertebra measures 

 2-2 centimetres wide by 1*8 centimetre deep, the transverse mea- 

 surement through the middle of the centrum is only 7 or 8 milli- 

 metres* The form of the centrum is thus almost Teleosaurian in 

 its constriction. The second centrum has a slight tendency to be 

 flattened on the ventral side, which is less marked in the third, 

 while the fourth appears to carry a slight median ridge. The 

 parallel ligamentous striations seen on the anterior border of the 

 first vertebra are necessarily absent from the subcrenulate junc- 

 tions of the succeeding vertebrae. 



The neural spine is very thin and is broken away in every spe- 

 cimen (fig. 13, ns), so that the greatest height from the base of the 

 centrum, as preserved, is only 3*5 centimetres. The third and fourth 

 vertebrae develop additional lateral spines, one on each side of the 

 median vertical neural spine, and these spinous processes directed 

 outward and upward, termed metapophyses (fig. 13, m), correspond to 

 those seen in the lumbar and caudal vertebrae of many mammals and 

 the sacrum of Megalosaurus. Metapophyses are indicated on the 

 second vertebra by long blunt ridges, and on the fifth vertebra by 

 short ridges which are almost tubercles. 



The transverse process from the first sacral vertebra (fig. 14, l) is 

 given off from the sides of the neural arch, and is directed obliquely 

 upward and backward, terminating outward in a narrow vertically 

 compressed process of a wedge shape, constricted in the middle, 

 flattened behind, sharp in front, concave below, and convex above, 

 with a strong tubercle in the middle of the upper surface. 



The transverse measurement between the extremities of the pro- 

 cesses is 33 millimetres. The antero-posterior extension of the 

 process along its outer border is 12 millimetres, and the correspond- 

 ing measurement at the middle of the constriction of its sides is 7 

 millimetres. 



The transverse process of the second vertebra is in the anterior 

 half of the vertebra, has a strong base posteriorly, and forms a ver- 

 tically elongated, somewhat flattened, articulated surface, which is 

 1*9 centimetre deep in front, where the vertical border is concave, 

 and 1*1 centimetre deep behind, so that the upper and lower sur- 

 faces converge posteriorly (fig. 14, 2). Its antero-posterior extent is 

 1 centimetre. The articular surface is irregular in contour, well 

 defined, and does not extend to quite the same upward elevation as 



