NILS ROSEN, STUDIES ON THE PLECTOGNATHS. 3 



Balistid ae. 



Thilo has called attention to the relation between the 

 ventral body-muscles of Monacanthus and the pelvic and 

 postclavicular bones. A paired portion of the inuscles acts as 

 erector of the pelvic bone. 



I have studied the muscles of Balistes vetula (Fig. 2, 15 and 

 16). The dorsal muscles show distinct nryomers, representing 

 the portions a and b of Maurer's diagram. In the former 

 the direction of the fibres is from caudally-dorsally to cra- 

 nially-ventrally, in the latter from caudally-ventrally to cra- 

 nially-dorsally. Supracarhwl muscles are present behind the 

 second dorsal fin. The ventral muscles show two portions 

 corresponding to ra. obliquus superior and m. obliquus injerior. 

 M. obliquus superior lies caudally dorsal to ra. obl. inf. In 

 the praecaudal region m. obliquus injerior is strongly enlarged 

 and covers ra. obliquus superior. The fibres of ra. obliquus 

 superior and ra. obliquus injerior have the usual directions, 

 as shown in Fig. 2. In this figure a part of ra. obliquus in- 

 jerior has been cut off in order to show the underlying m. 

 obliquus superior. Both muscles are distinctly metamerical 

 except the most anterior part of ra. obliquus injerior. 



The anterior part of ra. obliquus injerior is attached to 

 the pectoral arch and to the postclavicle. Another portion 

 of the same muscle passes inside of the first inclinator muscle 

 of the anal fin and is inserted along the ventral börder of 

 the caudal part of the pelvic bone. In the caudal region the 

 ventral ends of the myocommas make a bend and run for a 

 short distance transverse or caudal-ventral as in the portion 

 c of Maurer's diagram. The fibres have the same direction 

 as in ra. obl. inf. I do not think that this part represents 

 the portion c. I have found a very interesting muscle pass- 

 ing transversely from the posterior end of the postclavicle 

 and from the interiör side of the lateral body-fascia to the 

 pelvic bone. It is inserted into a part of the ventral börder 

 of this bone outside of the portion of ra. obliquus inf. that 

 is inserted along the same bone. To judge from the close 

 relation of the fibres of this muscle at their origin to the 

 fibres of ra. obliquus inf., I consider it very probable that 

 this transverse muscle is a portion of ni. obliquus inf. which 

 has become to a certain extent distinct. 



