88 



AMPHIOXUS. 



Ti ri<-,nf>Tinrrl g.nrl apjnal cord, connective tissue partitions or septa 

 ar ise, which, running outwards to the skin, divide the gre at 

 lateral muscles of the body into muscle-segments or myotome s 



(Fig.ll,K, andFig.l2,x.) 

 The attachments of these 

 septa to the skin are indi- 

 cated by a series of >- 

 shaped markings, very 

 clearly seen on the sides 

 of the animal along its 

 whole length (Fig. 11). 



The only other skele tal 

 str actures of importan ce 

 are a series of elastic chit i- 

 n ous rods, supporting t he 

 side walls of the pharynx ; 

 and an oval hoop,^ sur- 

 rou nding the rprint.Tn. 



The great lateral mus- 

 cles, noticed above, are the 

 most important part of the 

 muscular system. They 

 form the side walls of the 

 body along its whole length 

 (c/. Figs. 12 and 13), 

 and are divided, as already 

 described, into muscle seg- 

 ments or myotomes by the 

 connective tissue septa. 

 The muscle fibres of each 

 myotome run longitudi- 

 nally, i.e. parallel to the 

 axis of the body, the fibres 

 taking origin from the 

 connective tissue septa. 

 The myotomes have been 

 found to be sixty-one on 

 each side of the body in a 

 considerable number of specimens, and it seems probable 

 that this number is constant. The myotomes of the two sides 



