122 ARTICULATIONS OF THE TRUNK AND HEAD. 



vertebrae and firmly attached to both ; the direction of the obliquity being 

 reversed in each successive layer, in one stretching downwards from right to 

 left, and in the next from left to right. Some of the fibres also are nearly 

 horizontal. The central part of the fibro-cartilage is a pulpy and elastic 

 material which, when the pressure which confines it is taken off by cutting 

 through the intervertebral substance, rises up so as to assume a conical form. 

 It is then seen to be of a lobate structure, and, examined under the micro- 

 scope, exhibits a finely fibrous and homogeneous matrix, with numerous 

 spherical and elliptical cells, some of them resembling cartilage corpuscles, 

 others larger and of various appearance. 



It is now generally admitted that the pulp of the intervertebral disc is a persistent 

 part of the chorda dorsalis ; homologous, therefore, with those larger vestiges of the 

 chorda dorsalis which occupy the biconical cavities between the bodies of the vertebrae 

 in fishes. According to Luschka, there is present in each disc a synovial cavity, and 

 the lobes of the pulp are synovial villi, similar to those which are to be found in the 

 knee and shoulder joints, but of larger size, and occupying the whole cavity; and it 

 is worthy of notice that in like manner secondary cavities, developed within the 

 chorda dorsalis, are found in the intervertebral substance in many fishes. The same 

 writer describes small synovial sacs, in the cervical region, in those parts of the discs 

 which are attached to the lateral elevations of the bodies of the vertebrae. Occasionally 

 the pulp of the discs projects backwards, through the surrounding laminae, so as to 

 form a slight projection into the spinal canal. (Luschka, "Die Halbgelenke des 

 Menschlichen Korpers," Berlin, 1858, p. 84.) 



A thin cartilaginous layer, incomplete towards the circumference, covers 

 the surfaces of the vertebrae and gives attachment to the discs. Ex- 

 cluding from consideration the first two vertebras, between which it does not 

 exist, the intervertebral material forms in length about a fourth of the movable 

 part of the column. The dorsal part of the column has, comparatively with 

 the length, a much smaller proportion than the cervical or lumbar parts. 



The discs in the cervical and lumbar regions are thicker in front than behind, and 

 it has been determined that the convexity of those portions of the column is due to 

 them much more than to the bodies of the vertebrae, while the arching of the dorsal 

 portion, on the contrary, is rather owing to the shape of the bones. (W. and E. 

 Weber, " Mechanik der menschl. Gehwerkzeuge," p. 90, et seq., Gottingen, 1836.) 



The anterior common ligament is a strong band of fibres, which is placed 

 on the front of the bodies of the vertebrae, and reaches from the atlas to the 

 first bone of the sacrum, becoming broader as it descends. It consists of 

 longitudinal fibres which are dense, firm, and well marked. The superficial 

 fibres extend from a given vertebras to the fourth or fifth below it ; the fibres 

 subjacent to these pass over the bodies of several vertebrae ; whilst the 

 deeper ones pass only between adjacent vertebras. The band is thicker 

 towards the middle of the bodies of the vertebrae than at their margins, or 

 over the intervertebral cartilages ; by which means the transverse depressions 

 of the bodies are filled up, and the surface of the column rendered more 

 even. The fibres adhere more closely to the margins of the bones than to 

 the middle of their bodies, and still more closely to the in vertebral carti- 

 lages. Upon the sides of the bodies there are some fibres which are thin 

 and scattered, and reach from one bone to another. 



The posterior common ligament is situated within the spinal canal, and is 

 attached to the posterior surface of the bodies of the vertebras ; it extends 

 from the occiput to the sacrum. It is smooth, shining, and broader at the 



