108 



THE ELASMOBRANCH FISHES 



region of Chlamydoselachus the adductors diminish in size from behind for- 

 ward, so that, in addition to the absence of one from the hyoidean arch, there 

 is but slight evidence of a first branchial adductor. 



Hypobranchial Musculature 



The hypobranchial or ventral longitudinal muscles extend from the coracoid 

 cartilage forward under the branchial basket, and consist of the arcus com- 

 munes which continue forward from the pectoral girdle, the coracomandi- 



Fig. 110. Hypobranchial muscles. (From Max Fiirbriiigcr.) A. Scymnus. B. Heterodonlus 

 philippi. 



car., coracoarcualis muscle; c.hr., coracobranehialis; c.hy., coracohyoideus muscle; c.md., 

 coracomandibularis. 



hularis, lying in the middle line, the coracohyoideus at the sides of the cora- 

 comandibularis, and the deeper coracohranchiales extending to all the bran- 

 chial arches. All these muscles except the coracobranchials arise from the 

 first five trunk myotomes (fig. 102) as buds which migrate forward and me- 

 diad and take up their position under the branchial and buccal areas. The 

 coracohranchiales in Scyllium, according to Edgewortli (1903), are developed 

 from head myotomes. In the sharks the hypobranchials usually come to be 

 heavy round muscles, while in the rays they are more or less flattened. 



The arcus communes (see coracoarcualis, car., fig. 110) are separated by 

 mj^osepta (scriptores tendiniae) , much like other ventral bundles, into a vary- 

 ing number of segments in different forms. In Heterodontus philippi (fig. 

 110b) , for example, a single segment is produced, in Raja two, and in Scymnus 

 (fig. 110a) and a number of other types, five are present anterior to the girdle. 



