98 



A REVISION OF THE COTYLOSAURIA OF NORTH AMERICA 



no indications of a cleithrum. It is very evident that the coracoids in life were in 

 immediate contact along the median line, covered over by the prolongation of the 

 interclavicle. The scapulae curve upward at an angle of about forty-four degrees 

 from the plane of the coracoids. Possibly this angle has been slightly reduced by 

 pressure, but I think not. The scapulae are directed, not backward, as has been 

 supposed, but obliquely upward." 



The vertebral column: In No. 4424 American iMuseum there are 25 presacrals. 

 Between the twentieth and twenty-first there is a break, as the anterior portion of 

 the twenty-first is lost; so there is some possibility that the number was greater, but 

 this is very improbable. Williston gives twenty-three or twenty-four in his speci- 

 men No. 642 Univ. of Chicago, but the anterior cervicals are covered by the skull 

 and there is a break near the sacrum, so that his number is also uncertain. 



The atlas is unknown. 



The axis does not seem to have been very different from the succeeding ver- 

 tebrae. The spine was elongate anteroposteriorly, but not high. As all the vertebrae 

 bear ribs and are strikingly similar in form it is impossible to divide the column into 



Fig. 42. — Lower jaw of Can gustier ps- 

 X f . No. 4456Am. Mus. d, dentary; 

 sp , splenial; sa, surangular; a, articular 



Fig. 4}. — Captorhinus. xi- No. 4424 Am. Mus. 

 a, cervical vertebra?; b, cross-section of a dorsal vertebra; r, sacral 

 vertebra? ; d, humerus and radius; t , left side of pelvis. 



cervical, dorsal, and lumbar regions. All the vertebrae have low, rounded neural 

 arches, with wide zygapophyses. The anteroposterior and transverse diameters of 

 the neural arches are nearly equal. The transverse processes of the anterior verte- 

 bra; originate high up on the centrum and the side of the neural arch and stand out 

 almost at right angles. The articular face for the rib is elongate vertically; the 

 lower edge is attached near to the anterior edge of the centrum and is close to it, so 

 the face slants forward and inward, as in Diadectes and Labidosaurus. In the pos- 

 terior vertebrae the transverse processes are more slender and rod-like and originate 

 high up on the centrum. The body of the centrum is contracted slightly in the 

 middle portion, but there are no keels or ridges. Small intercentra were present 

 throughout the column. 



There are two sacral vertebra. The first has a large rib expanded distally and 

 directed straight out to the ilium. The second sacral is much smaller and its rib 

 appears to be very largely applied to the posterior surface of the distal half of the 

 anterior sacral rib. 



The caudal vertebra; have more slender arches and spines than the presacrals. 

 The first ones carry strong ribs anchylosed to the transverse process. These curved 

 downward sharply, showing that the tail was heavy at the base. Chevrons are 

 present in the anterior part of the column, but it is not known how far back they 

 extended. Williston estimates twenty-five vertebrae in the tail. 



