M. Serres on Glyptodon ornatus. 437 



at this point there existed certain conditions of mobility, which 

 were doubtless of but little extent, but of which the multiplica- 

 tion and complication of all these synarthroses accumulated at 

 the same point furnish a certain indication. The whole of this 

 organic construction, moreover, is in accordance with what I 

 have said above as to the partial flexibility of the carapace. 



The two coccygeal vertebrae of the sacrum present modifica- 

 tions corresponding with those of the ischium, with which they 

 are articulated. The first of these vertebrae, which is intimately 

 imitcd to that which precedes it, is placed nearly in a vertical 

 plane, slightly inclined from above downwards, and from before 

 backwards. The total height of the vertebra is 8 centimetres ; 

 its apex is about 3 centimetres distant from the carapace. The 

 spinous lamina which surmounts its arch presents posteriorly 

 two diarthrodial facets (articular apophyses), corresponding with 

 two facets of the following vertebra. 



The transverse apophysis, which is lamellar as in G. clavipes, 

 is placed at first in the same plane as the body of the vertebra, 

 but undergoes a slight torsion and becomes horizontal. It con- 

 ceals the transverse apophysis of the following vertebra, and 

 articulates therewith much more completely than in G. clavipes. 

 By its squarely truncated extremity it articulates with the pyri- 

 form synarthrodial surface which occurs on the inner face of the 

 ischium. 



The second coccygeal vertebra of the sacrum is placed in a 

 much more oblique plane than the preceding one. Hence the 

 body of this vertebra makes with that of the preceding one a 

 salient angle about equal to the sacral angle in man. In its 

 form the body of this vertebra exactly resembles that of the 

 caudal vertebrae. The rhachidian canal becomes suddenly much 

 less in diameter on reaching its level. The spinous apophysis 

 is no longer a lamina, but is rounded and obtuse. At its base 

 in front are articular apophyses corresponding to the two facets 

 borne by the arch of the preceding vertebra. 



It was of interest, with regard to the mechanism of the tail in 

 Glyptodon, to ascertain exactly the position of this vertebra with 

 relation to the caudal emargination of the carapace. A straight 

 line drawn from the centre of this emargination to that of the 

 cephalic notch passes through the apex of the salient angle which 

 this vertebra assists to form. The distance from the posterior 

 face of the body of the vertebra to the centre of the caudal 

 emargination is 0"125 metre. The distance from the apex of 

 its spinous apophysis to the same point is O'OSO m. 



The transverse apophysis passes entirely beneath that of the 

 preceding vertebra. But, contrary to what occurs in G. clavipes, 

 it passes this, and articulates by its superior face, which is 



