VERTEBRAL COLUMN. 67 



B. 86. Portion of the precaudal vertebral column including six 

 vertebrae of a Skate (Raja batis). 0. 0. 237 D. 



B. 87. Three portions of the vertebral column of a Kay (Raja 

 clavata) taken respectively from the anterior, median, and 

 posterior regions of the body. The column is formed in its 

 anterior part (upper specimen) of a single rigid mass of carti- 

 lage, in which the only indication of segmentation is afforded 

 by the nerve-foramina (31 pairs) on each side. The charac- 

 ters of this part of the column have probably arisen in 

 response to the demand for additional strength to support the 

 enlarged pectoral fins. Somewhat posterior to the shoulder- 

 girdle, the segmented notochord appears ; . its upper and 

 lateral surfaces are enveloped by basi- inter- and supra- 

 dorsalia and basiventralia (the latter are at first continuous 

 with the basidorsalia) . In the middle specimen the transition 

 from trunk to tail is shown ; the basiventralia become 

 separated from the basidorsalia, migrate to the ventral aspect 

 of the notochord and there, with the addition of inter- 

 ventralia, form the haemal arches. The interdorsalia are 

 gradually suppressed. The lower specimen shows the 

 degenerate condition of the tail. 



Hasse, Nat. Syst. Elasmobr. 1882, p. 168. 



AECHCENTROUS. 



B. 88. Portions of the vertebral column of Lepidosteus osseus. 

 The vertebral bodies are opisthocoelous and developed 

 entirely from the arches without invasion of the chordal 

 sheath by skeletogenous cells (archcentra). In the adult 

 the notochord is altogether suppressed. The three upper 

 specimens are taken from the precaudal region, the two 

 lower from the caudal. 



Balfour & Parker, Phil. Trans., vol. clxxii. 1882, p. 386. 



B. 89. Portions of the trunk region of the vertebral column of 

 a Cod (Gadus morrhua). 



Each vertebral body consists of a deeply biconcave disc 

 of bone, smooth and hard upon its concave surface, but of 

 looser texture outside. It is attached to the bodies of 

 neighbouring vertebra by the edges of its cavities by means 



F2 



