1918] Davidso)! : The MiiscuJafure of Hcptcnichus Diaculattts 155 



cJtHS, divides the veutral constrictor group in Acaxfhias into six parts 

 corresponding to those of the dorsal group. The part which he calls 

 the first, is known as part of the second ventral constrictor by Vetter. 

 Marion names the part inserting on the first visceral or mandibular 

 arch tlie first, and that on the hyoid arch the second. There seems 

 to be some doubt that these are separate muscles. Insertion is not 

 an absolute criterion, as the second dorsal constrictor is inserted 



Fig. 2. Horizontal section through 

 gill, Heptnnchnn maeulattis (X M>)- ad., 

 adductor of the branchial arch; af.. 

 afferent artery; hr., branchial ray; csd., 

 dorsal constrictor muscle; eb., epibranch- 

 ial cartilage; t'fc.\ fourth efferent col- 

 lector artery; efc.^, fifth efferent col- 

 lector artery; ex. h., extrabranchial car- 

 tilage; ^. a., anterior gill-filament; ^. /»., 

 posterior gill-filament; ibd., dorsal inter- 

 branchial muscle; n. nerve. 



ad.-^ 



both on the first and the second arches. In Heptanchus maculatus 

 it is not possible to demonstrate a division of the first and second veu- 

 tral constrictors as clearly as is shown for Acantliias by Marion (p. 9, 

 fig. 5). The following condition is found in Heptanchus maculatus. 

 The first and second ventral constrictors appear to be united. The 

 second ventral constrictor (csv.-) extends from the mandibular sym- 

 physis to the anterior border of the first gill-slit. The fibers of both 



