20 



THE BONES AND JOINTS. 



Fisr. 6. 



IV. Stuuctuee of the Vertebrae ^ (Fig-s. 6 and 7). 



Each vertebral body consists of a cylinder of compact bone, which 

 is directly continued into the bony substance of the arch. In the 

 interior of the cylinder is found an isolated persistent vestige of the 

 chorda d or salis (CIi): this is surrounded by cancellous bone [c), which 

 extends backwards towards the articular head and forwards directly 

 into the articular cartilage, compact bone being- absent in these 



parts. In a transverse section of a ver- 

 tebral body the following parts are seen 

 (Fig". 6) : — a. An outer layer of compact 

 bone [0) (the transverse section of the 

 above-mentioned cylinder), which is formed 

 of parallel lamellae of varying thickness. 

 These, according* to Geg-enbaur, and as I 

 can confirm, are arrang-ed in well-defined 

 groups, each of five to eight lamellae. 

 The number of the secondary lamellae 

 increases with the age of the animal. 



b. In the interior, in the form of a cylin- 

 der, is the remnant of the chorda dorsalis. 

 It consists of a double sheath {Ch') and 

 contents (C//-) composed of chorda-cells. 



c. Immediately around the persistent por- 

 tion of the chorda lies the central part of the 

 vertebral body, formed by transformation 

 of the vertebral cartilag-e and of the bases 

 of the orig-inal cartilaginous arches. At 

 each side of the chorda are large marrow- 

 spaces (f), filled with cells, from which 

 proceed narrower canals, winding in various 



Longitudinal section tiirougii the directions, and auastomosiug freely with 



posterior lialf of the body of a , ^ l^ ^ c ^ ^ ^ • i rm 



vertebra of Rami cscuienta. ouc anothcr Doth Dciore and behmo.. 1 heir 



a Cartilage of the head. walls are Constituted partly of true bone, 



c Cancellous bone. . 



o Shell of compact bone. partly of Cartilage. 



Transvei-se section through a ver- 

 tebra of Rana esculcnta, magni- 

 fied. 

 c Cancellous bone. 

 Ch Chorda dorealis. 

 Ch' Sheath of chorda dorsaHs. 

 o Compact bone on the upper 

 and lower surfaces of the 

 body. ^ 



Fig. 7. 



' Cf. Gegenbaur, (i) Uber Bau u. Entwickluiig der Wirbelsiiule bei Amphibien 

 iiberhaupt u. beim Frosch insbesondere. Abband. d. Naturforsch. Gesell. zu Halle, 

 vol. vi, 1 86 1 ; (2) Untersuch. zur vergleich. Anat. d. Wirbelsiiule bei Amphibien 

 u. Rept., Leipzig, 1862. As regards the adult animal I can bear out Gegenbaur's 

 observations. The scope and limits of this book forbid me to go further into the 

 developmental history. 



