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REPORT — 1855. 



On the Vertebral Homologies in Animals. 

 By Professoi- William Macdonald, 3LD., St. A?idrew's. 



When Goethe and Oken first pointed out the striking analogy subsisting between 

 the separate bony segments of the cranium of a deer which was accidentally picked 

 up in the Black Forest, and the different portions of the vertebral column, they evi- 

 dently adopted the usual definition of the vertebra, as then and still too commonly 

 followed in the medico-anatomical schools, as consisting of a body — transverse and 

 articulating processes with a bony ring terminating in a spinous process. The pre- 

 vailing expression in common language of the whole vertebral column being viewed 

 as the back-honp, long tended to obscure the investigation, and to some extent it still 

 impedes the adoption of more scientific and philosophic views. This was strongly 

 urged at the Association meeting at Cambridge in 1845. 



If a simpler definition of a Vertebra were adopted, there is little doubt that the 

 homologies of the bony segments of the vertebral column would be easily traced by 

 the anatomical student and comparative anatomist, and with that view it is proposed 

 to restrict the term vertebra, and thus define it to consist merely of the Body or 

 Centrum with the Transverse Process or Diapophysis and the Mesapophysis. Thus 

 restricted, it will form a portion or segment of the Central Stem on which the other 

 laminae are developed, and the skeleton constructed. On this ground the Professor 

 repudiates the common appellation of the back-bone, and also on the ground of its 

 consisting of many separable segments, each consisting of several bones. 



First, the Central Stem or Caulon, in man, consists of several classes of 

 bones or vertebrae, and extends from the nasal spine of the frontal bone, along 

 the basis cranii, down the bodies of the vertebral column and sacrum to the 

 simple condition in the coccyx. 



In the lower animals, where the tail exists, the caulon is extended to the tip. 



It is necessary to explain a few of the terms used in the present communication 

 in order that the subject may be understood as intended. Lamina includes all the 

 bony branches extending around the great cavities of the body arising from the 

 caulon or central stem, viz. the ribs, bones of the face, as well as the limb-bearing 

 zones, whether these support the maxillte, the arm or the leg ; also the perineural 

 arches forming the tunnel for the cerebro -spinal axis. Following the example of 

 the distinguished Hunterian Professor of the Royal College of Surgeons, Professor 

 Owen, Dr. iSIacdonald feels inclined to adopt the Greek etymology in constructing 

 the form of the nomenclature ; but as it may be viewed as too pedantic, he also 

 uses the names already adopted by others, and also such as can be made up of the 

 common expression. 



