VERTEBRAL COLUMN. 63 



to show the pointed extremity of the notochord surrounded 

 by the cranial cartilage. 0. 0. 230 c. 



B. 70. Anterior portion of a Glutinous Hag (Mifxhie f/ltitinosa). 

 showing the notochord. 0. C. 230. ffunterian. 



B. 71. Portions of the vertebral column of a Sea -Cat (Chimcera 

 monstrosa). The column, although without any suggestion 

 of vertebral bodies, is potentially chorda-centrous owing to 

 the invasion of the chordal sheath by cells from the skeleto- 

 genous layer. The continuous notochord is surrounded by 

 a delicate elastica externa and a very thick elastica interna 

 (chordal sheath). The latter is to a considerable extent 

 cartilaginous, and is divided into an inner and outer layer 

 by a series of narrow calcified rings, contiguous with one 

 another and far more numerous than the basi-dorsalia. The 

 dorsal arches are composed of basi-dorsalia, inter-dorsalia, 

 and supra-dorsalia; towards the middle of the body the 

 supra-dorsalia disappear, and in the tail-region they are 

 followed by the inter-dorsalia. The ventralia consist of a 

 double row of small irregular cartilages. A certain number 

 of the anterior arcualia are fused together and enlarged to 

 provide a support for the anterior spine of the dorsal fin. 

 The skull articulates to the vertebral column by a diarthrodial 

 joint. 



The upper specimen is the anterior portion of the vertebral 

 column, in it some of the dorsalia are outlined in black. 

 The next specimen (part in sagittal section) is taken from 

 the middle of the body; beneath is a transverse section 

 from the same region. The two lower specimens are from 

 the tail. 



Hasse, ' Natiirliches System der Elasmobranchier/ Jena, 

 1882, p. 25. 



B. 72. Specimens of the calcareous rings from the chordal sheath 

 of a Sea-Cat (Chimcera mediterranea). The rings have the 

 form of narrow fibrous bands, with a deep concavity running- 

 round their outer side. They are composed of dense 

 calcified connective tissue, the fibres and cells of which are 

 packed closely together with their long axes mainly parallel 



