37g on the anatomy of amphioxus lanceolatus. 



Anatomical Description of the Amphioxus. 



Osseous System. 



Neuro-skcleton. — The osseous system, properly so called, 

 consists of a " chorda dorsalis " tapering at both ends, without 

 the vestige of a cranium, and of a dorsal and ventral series of 

 cells, the germs of superior and inferior interspinous bones 

 and fin-rays. The " chorda dorsalis " consists of sixty to 

 seventy vertebras, the divisions between which are indicated 

 by slight bulgings, and lines passing obliquely from above 

 downwards on the sides of the column. In this way a separa- 

 tion into individual vertebrae is rather indicated than proved 

 to exist ; for although the column has certainly a tendency to 

 divide at the points above mentioned, yet that division is 

 rather artificial than natural. There is no difficulty in 

 ascertaining above sixty divisions, those at each end above 

 the number stated run so much into one another that no 

 correct result can be obtained. 



The chorda dorsalis is formed externally of a fibrous sheath, 

 and internally of an immense number of laminae, each of 

 the size and shape of a section of the column at the place 

 where it is situated. When an}^ portion of the column is 

 removed, these plates may be pushed out from the tubular 

 sheath, like a pile of coins. They have no great adhesion to 

 one another, are of the consistence of parchment, and appear 

 like flattened bladders, as if formed of two tough fibrous 

 membranes pressed together. 



As the fibres of the sheath are principally circular, provi- 

 sion is made for longitudinal strains on the column by the 

 addition of a superior and inferior vertebral ligament, as 

 strong cords stretching along its dorsal and ventral aspects. 

 The superior ligament lies immediately under the spinal cord, 

 and may be recognised as a very tough filament, when the 

 column is torn asunder, or some of the vertebrae removed. 



