SEETAL HOMOLOGIES OF THE VEETEBE.E. 



283 



APPENDIX C. 



TRUE TRANSVERSE 

 PROCESS 



FORAMEN TRANS- 

 VERSARIUM 



COSTAL PROCESS 

 XEURO-CENTRAL SYNCHONDROSIS 



CERVICAL 



i^^ TRUE TRANS- 



VERSE PROCESS 



COSTAL PROCESS 



RACIC 



NSVERSE 

 ROCESS 



FORAMEN TRANSVERSARIUM 



NEURO-CENTRAL SYNCHONDROSIS 



RIB 



LUMBAR 



SERIAL HOMOLOGIES OF THE VERTEBRAE. 



It is a self-evident fact that the vertebral column consists of a number of segments or verte- 

 brae all possessing some characters in common. These vertebrae or segments undergo modifications 



according to the region they oc- 

 cupy and the functions they are 

 called upon to serve, so that their 

 correspondence and identity is 

 thereby obscured. There is no 

 difficulty in recognising the homo- 

 logy of the bodies and vertebral 

 arches throughout the column. 

 According to some anatomists the 

 vertebral arch is the more primi- 

 tive element in the formation of a 

 vertebra, whilst others hold that 

 the bodies are the foundation of the 

 column. Be that as it may, we find 

 that in the higher vertebrates, at 

 least, the bodies are the parts which 

 most persist. They are, however, 

 subject to modifications dependent 

 on their fusion with one another. 

 This occurs in the cervical part 

 of the column where the body 

 of the first cervical or atlas has 

 for functional reasons become 

 fused with the body of the 

 second or epistropheus to form 

 the dens of that segment. For 

 similar reasons, and in association 

 with the union of the girdle of 

 the hind -limb with the column, 

 the bodies of the vertebrae which 

 correspond to the sacral segment 

 become fused together to form a 

 solid mass. In the terminal por- 

 tion of the caudal region the bodies 

 alone represent the vertebral seg- 

 ments. 



As regards the vertebral arch, 

 this in man becomes 

 deficient in the lower 

 sacral region, and absent 

 altogether in the lower 

 coccygeal segments. The 

 spinous processes are 

 absent in the case of the 

 first cervical, lower 

 sacral; and all the coc- 

 cygeal vertebrae, and 

 display characteristic 

 differences in the cervi- 

 cal, thoracic, and lum- 

 bar regions, which have 

 been already described. 

 The articular processes 

 (zygapophyses) are 

 secondary develop- 

 ments, and display great 

 diversity of form, deter- 

 mined by their func- 

 tional requirements. It 

 is noteworthy that, in 

 the case of the upper 

 front of the foramina of exit of 



COSTAL ELEMENT (RIB) 

 SACRAL 



.!. MKNT 



OCCASIONAL FORAMEN 

 IHAXSVERSARIUM 

 NEURO-CENTRAL SYNCHONDROS] 



COSTAL ELEMENTS 



80. DIAGRAM TO ILLUSTRATE THE HOMOLOGOUS PARTS OF THE VERTEBRA. 



he bodies are coloured purple ; the vertebral arch and its processes, red ; the costal 

 elements, blue. A, from above. B, from the side. 



two cervical vertebras, they are so disposed as to lie in 

 upper two spinal nerves, and by this arrangement the weight of the head is transmitted to 

 solid column formed by the vertebral bodies, and not on to the series of vertebral arches. 1 _t IB m 

 regard to the homology of the transverse processes, so called, that most difficulty a 



