298 



ANATOMY OF VERTEBRATES. 



1S4 



1^ 



Mammalian type 



vertebra, from the 



thorax. 



185 



in large Ruminants is referable to the ^ splauclmoskeleton ; ' the 

 ossified tendons in some small Musk-Deer to the 

 ^ scleroskeleton.' 



In the Mammalian class the centrum, figs. 141, 

 184, <?, coalesces -with the neural arch, ib. w, 

 throughout the vertebra3 of the trunk. In the 

 seven anterior vertebra?, fig. 185, i-7, the pleur- 

 apophyses are short and commonly coalesce with 

 the centrum and diapophysis, circumscribing the 

 lateral foramina for the ' vertebral ' arteries. In 

 the Monotremes they retain, as in Reptiles, their 

 individuality, fig. 186, a. In Cetacea the inter- 

 space between the cer\dcal par- and di-apophyses 

 is not always closed by bone. Occasionally the pleurapophyses 



of the seventh, fig. 185, A, 

 h, and, more rarely, also of 

 the sixth, «, vertebrae, mani- 

 fest their rib-like nature by 

 increase of length, and free- 

 dom of articulation, even in 

 Man; but these segments 

 are not completed by the 

 liaemapophyses and haemal 

 spine. This resumption of 

 type takes place in the eighth 

 vertebra, ib. c, d\ and the 

 dorsal series of vertebras here 

 begins, as a rule, in Mam- 

 mals. The most marked ex- 

 ception occurs in the Ai 

 (^Bradi/pus tridactylus) ; and 

 supporting the pleurapophyses, 

 a, h, be regarded as homologous 

 with the first two dorsals in other 

 Mammals, the exception is so far 

 saved : but the presence of short 

 pleurapophyses in all the cer- 

 vical vertebrae and their occa- 

 sional developement in the last 

 two, as in fig. 185, A, support the 

 recognition of the tenth verte- 

 bra in the Three-toed Sloth, ib. b, 

 10, c, d, as the first dorsal. The 



cervical vertebn-e, Ornithorliyncl.us. plcUrapOphySCS of thc dorsal VCr- 



Cervical vertebrae, A Man, B Sloth. 



if the vertebra, fig. 185, B, 8, 9, 



186 



