THE BOX1;S AND JOINTS. 



Kir. 6. 



IV. STRUCTURE OF THE VERTEBRAE * (Figs. 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 dorsalis (C ft]: 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 (#) (the transverse section of the 

 above-mentioned cylinder), which is formed 

 of parallel lamellae of varying thickness. 

 These, according to Gegenbaur, and as I 

 can confirm, are arranged 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 (Cfi) 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 cartilage and of the bases 

 of the original cartilaginous arches. At 

 each side of the chorda are lai'ge marrow- 

 spaces (?), filled with cells, from which 

 proceed narrower canals, winding in various 

 directions, and anastomosing freely with 

 one another both before and behind. Their 

 walls are constituted partly of true bone, 

 partly of cartilage. 





Transverse section through a ver- 

 tebra of liana esculenta, magni- 

 fied. 



c Cancellous bone. 



L'li, Choi-da dorsalis. 



C/i' Sheath of chorda dorsalis. 



o Compact bone on the upper 



and lower surfaces of the 



body. 



Fig. 7. 



Longitudinal section through the 

 posterior half of the body of a 

 vertebra of liana esculenta. 



a Cartilage of the head. 



c Cancellous bone. 



o Shell of compact bone. 



1 Cf. Gegenbaur, (i) Uber Bau u. Entwicklung der Wirbelsiiule bei Amphibian 

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

 vol. vi, 1861 ; (2) Untersuch. zur vergleich. Anat. d. Wirbelsaule bei Amphibien 

 n. Kept., 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. 



