196 



1012. The fore part of the osseous thoracic-abdominal box of a large Tortoise (Tes- 

 tudo elephantopus}. 



It shows the modifications of the ordinary elements of a vertebra and their coalescence with 

 dermal bony plates, to which this singular structure is due. The upper piece or key of the 

 arch is formed by a horizontal plate of bone, developed in the integument, and connate with 

 the summit of the neural spine. The pleurapophyses of the same vertebra are similarly con- 

 nate with expanded and flattened costal plate, which is articulated by suture to the sides of the 

 neural plate. The distal or inferior extremity of the pleurapophysis is articulated by suture 

 to the haemapophvsis, or sternal rib, which expands as it descends into a broad quadrate plate 

 articulated by suture partly to the haemal spine, or ' entosternum,' partly to its fellow. The 

 modified elements of the neural and haemal arches here preserved belong to the first vertebra 

 of the carapace, or second ' dorsal ' vertebra. The centrum has been removed, showing the 

 articular surfaces of the neurapophyses and pleurapophyses, divided each into anterior and 

 posterior facets, the latter being those which alone articulated with their proper centrum. 

 The short pleurapophyses of the first dorsal vertebra are retained, united by their sutures to 

 those of the second vertebra. The anterior median and anterior marginal pieces of the cara- 

 pace which articulate with the anterior borders of the costal plates of the first vertebra of the 

 carapace, and the two anterior pieces of the plastron called ' episternals,' are also preserved in 

 this specimen. 



Presented by Prof. Owen, F.R.S. 



1013. A posterior segment of the same thoracic-abdominal box of the Testudo ele- 

 phantopus. 



It shows the union of the left pleurapophysis of the sixth vertebra of the carapace with its 

 expanded hsemapophysis, which articulates with its fellow of the opposite side without the 

 intervention of a haemal spine : these expanded elements are termed ' hyposternals,' and the 

 plastron is terminated behind by two smaller pieces of the same series of elements called 

 ' xiphisternals.' With this preparation are also preserved the costal plates connate with the 

 left pleurapophyses of the third, fourth and fifth vertebrae of the carapace, showing the slen- 

 der elongated free portion of the rib, which supports the head, and the alternate increase of 

 breadth in the proximal and distal portions of the costal plates. Three of the dermal bones 

 called ' marginal pieces ' of the carapace are also preserved on the left side. 



Presented by Prof. Owen, F.E.S. 



1014. The posterior extremity of the same carapace. 



It consists of the neural arches of the seventh and eighth vertebrae of the carapace, with 

 the corresponding connate neural plates, and the three median dermal pieces which succeed 

 and are serially homologous with those plates. Three of the marginal pieces on each side 

 complete this end of the carapace. With these parts are preserved the neural arch and pleur- 

 apophyses of the first sacral vertebra. The neural spine of this vertebra articulates by a 



