52 TRUNK VERTEBRA. [chap. 



metapophyses are rudimentary, and there are no distinct 

 anapophyses. 



As there is no sacrum in the Cetacea the lumbar region 

 passes directly into the caudal, and they can only be dis- 

 tinguished by the presence of " chevron bones " in the 

 latter. 



The thoracic vertebrae vary in number from 9 in Hyper- 

 oodon, to 15 and occasionally 16 in some Fin- Whales 

 {Balamopterd), and the lumbar vertebrae from 3 in Inia (the 

 Amazonian fresh-water Dolphin) to 24 or even more in some 

 of the true Dolphins (Delphinus). 



The bodies are short in the anterior part of the thoracic 

 region, but posteriorly become more or less elongated and 

 cylindrical. Their terminal epiphyses are strongly ossified 

 disks, very distinct in young animals, but coalescing com- 

 pletely with the rest of the body in adult age. The spinous 

 processes are high and compressed. The zygapophyses are 

 very little developed, and only found in the anterior thoracic 

 region. The metapophyses are distinct (see Fig. 20, m\ 

 placed at first near the ends of the transverse processes, 

 but gradually rising on the arch, are ultimately transferred 

 to the sides of the anterior edge of the neural spine, from 

 which they project forwards, clasping between them the 

 hinder edge of the spine of the vertebra in front. 



In most Cetacea the transverse processes in the anterior 

 thoracic region arise rather high on the side of the neural 

 arch of the vertebra, but in the hinder part of the same 

 region become gradually placed lower, until finally they are 

 transferred to near the middle of the side of the body, 

 which position they occupy in the lumbar region (see Fig. 

 20). The transverse processes of the lumbar vertebrae are 

 thus evidently serially homologous with the transverse pro- 

 cesses of the anterior dorsal vertebrae, which, in their turn, 



