191SJ Davidson: The Musculature of Heptanchus maciUatus 169 



tudinal bundles are divided by connective tissue septa, the myosepta 

 into muscle segments, which externally present a zigzag appearance. 

 At the lateral septum there is a V which points anteriorly. The two 

 near the median ventral and dorsal lines point posteriorly. The 

 muscle segments do not extend directly in, as they appear to extern- 

 ally, but each extends far posteriorly and anteriorly in the direction 

 of the V's, giving to each segment an irregular form. The anterior 

 and posterior extensions of the muscle segments are in the form of 



Pig. 11 Fig. 12 



Figs. 11 and 12. Cross sections through dorsal fin and caudal regions (X %). 

 c. /'., caudal fin; d.f., dorsal fin; I., lateral muscle bundle; I. d., latero-dorsal 

 bundle; I. I., lateral line; I. v., latero-ventral bundle; m. d., medio-dorsal bundle; 

 m. v., medio-ventral bundle. 



cones so that in cross section they have the appearance of concentric 

 rings. 



Dorsally the musculature is the same in the tail and in the trunk 

 except for a difference in the sharpness of the angles of the V's. The 

 ventral musculature shows a much more extensive change in the trunk. 

 The voluminous organs of the body cavity greatly effect the muscles 

 of the body wall, causing them to form a very thin layer. The V's 

 are not sharp and the connective tissue septa pass more directly 

 inward, forming no cones. This greatly changes the appearance of a 

 cross section, since in it no concentric rings of muscle are formed. 



