326 Royal Society : — 



slight traces of ossification, as in HexancJnis and the anterior ver- 

 tebra of Ileptanchus, wliilst they may be almost wanting in others 

 pretty well ossified (Leptocephalus, Tlehnichthys, Centrophonis). 



3rd. The ossification of the cartilaginous vertebral bodies formed 

 out of the sheath of the chorda never begins at the surface, but 

 always in their interior, and also in their middle region, and is (as far 

 as I know, without exception) in the first instance a calcified fibro- 

 cartilage, or what I call a fibrous bone. 



4th. The first osseous parts have the form of thin rinys (Heji- 

 tunchus, anterior vertebra), wbich afterwards assume that of hollow 

 and thin douhle cones {Heptanchus, posterior vertebra, Centrophorus). 



5th. Tbe growth of these double cones, which are the real osseous 

 vertebral Ijodics, when once they have assumed their whole length, 

 takes place especially at their outer side, through the addition of 

 calcified cartilaye (chondriform bone, Williamson ; Knorpel-KnocTien 

 in German), which is formed from the outer chordal cartilage of the 

 vertebral body. In addition to this, the osseous double cone thickens 

 also at the expense of the cartilage inside of it, but in a much 

 smaller degree. 



Gth. In some cases the outer growth is everywhere the same, and 

 in this manner stronger double-coned vertebral bodies of uniform 

 thickness are formed. In other cases the growth is in some parts 

 more active than in others, and vertebral bodies then originate with 

 outer ridges and lamellas {Jleptanchus, Raia, Carcharias, Mustelus, 

 Galei(s). In one single histance the ossification of the outer cartilage 

 takes place in such away that the exterior parts of the vertebral bodies 

 are formed by alternating circles of chondriform bone and cartilage 

 (Squatina). 



7th. With regard to the extension of this growth of the vertebral 

 bodies formed by the ossification of the sheath of the chorda, it is to 

 be remarked that in some cases the whole, or nearly the whole sheath 

 of the chorda ossifies, as in Sqna/ina and the Raiidi3e. In other cases 

 greater or lesser parts of the primitive cartilage, inside and outside 

 the vertebral body, remain in their i)rimitive state (Squali). 



2. S/rnU. 



In some instances even the sheath of the cranial 'part of the chorda 

 ossifies in its hindermost jiart, and fo?-ms a true vertebral body 

 for the occipital vertebra, which entirely corresponds to those of 

 the column. This has been observed by me as yet in Lepto- 

 cephalns and several Squalidee ; but it is extremely probable that 

 the basilar occipital of all osseous fishes, viz. that part of this 

 bone which resembles a common vertebral body, is developed quite 

 in the same way. 



C, On the manner in which the outer ossifying layer is concerned 

 in the formulion of the bodies of the vertebrce. 



1st. In those cases where the outer ossifying layer, viz. that layer 

 in which the cartilaginous arches are developed, takes j)art in the 

 formation ol" the vertebral bodies, there arc to be distinguished two 



