ZOOGENY. 369 



2100. The vertebrae have originated through polar 

 rej^etitioft, through the muscular cysts. 



2101. In addition to the series of vertebrae on the 

 back, a vertebral column is formed moreover along the 

 ventral surface, and without doubt there only where the 

 air-organ, the branchia or lung, is situated. This inferior 

 vertebral column is the breast-bone or sternum. 



2102. All the systems, even those that are of a 

 subordinate character in the animal, follow the direction 

 of the main vertebral column. The intestine, as well as 

 the vessels, are placed in accordance with it. Thus the 

 principal trunks of the vessels take their rise along the 

 vertebral column, the other vessels being given off from 

 them in this situation, like the lymphatics frpm_the_ 

 intestine,. 



2103. The vascular ramules which surround the in- 

 testine and the skin, run out from a main stem, and 

 are directed in a symmetric manner downwards and 

 upwards (in the horizontal body of animals), or towards 

 the belly and back. 



2104. If new bony rings originate, they must also 

 take these directions. They accompany the vessels that 

 run in a circle, as the vertebral column accompanies the 

 vascular trunks. These annularly-disposed bony twigs 

 or apophyses constitute in the direction downwards the 

 ribs, in that upwards the vertebral arches. Anterior and 

 posterior to the vertebral column there consequently 

 originates a long canal formed by the bony rings. In 

 the anterior canal lie the galvanic or vegetative organs, 

 in the posterior or upper, the organs of light must be 

 situated " par excellence/' The former of these canals 

 is called the thoracic and abdominal cavity, the latter the 

 vertebral canal. The vertebral canal is not the bony or 

 medullary cavity itself, but it has been formed by several 

 bony cysts in the same manner as the thoracic cavity. 

 It consists of the body and the two arches. These are 

 thus posterior (superior) ribs. The vertebral canal has 

 the same signification as the thoracic cavity has; it is 

 only a posterior thoracic cavity. It therefore contains, 



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