PALATOQUADRATE WITH NEUROCRANIUM IN CCELACANTHIDS. 47 



personally examined, but they must be similar to those in 

 Chlamydoselachus. In the latter fish the most dorsal portion of 

 the dorso-mesial edge of the palatoquadrate forms tlie processus 

 m.etapterygoideus, a low ridge on the internal surface of this edge 

 of the apparatus forming the processus basalis (Allis, 1913). lx\ 

 the groove between these two ridge-like processes, the musculus 

 levator maxillae superioris, which is the homologue of the levator 

 arcus palatini of the Teleostei and Ganoidei, has its insertion, the 

 outer edge of the processus metapteiygoideus lying between the 

 surface of insertion of the levator muscle and the surface of origin 

 of the adductor mandibuhe. That branch of the nervus tri- 

 geminus that innervates the muscle runs posteriorly along its 

 external surface, and hence lies morphologically between the two 

 ridge-like processes. In Heptanchus and Hexanchus the con- 

 ditions unquestionably here difler only in that the processus 

 metapterygoideus has acquired articular contact with the laterally 

 projecting dorsal portion of the postorbital process, and that, in 

 consequence, the anterior portion of the levator maxillfe superioris 

 runs antero-ventrally beneath the overhanging portion of the 

 postorbital process, and hence internal to the processus meta- 

 pterygoideus. The nerve that innervates this muscle also runs 

 posteriorly internal to the latter process. The levator muscle of 

 these three fishes, and particularly that of Heptanchus and 

 Hexanchus, can accordingly have but little efiect in swinging the 

 palatoquadrate outward and upward, and Luther (1909) says that 

 this motion is impressed upon it by the musculus preorbitalis of 

 his descriptions, which is Vetter's (1874) muscle Add /3. This 

 action of this muscle is said to also throw the anterior end of the 

 palatoquadrate downward, the palatobasal (orbital) process sliding 

 downward along its articular contact with the orbital wall. Tiie 

 levator muscle then pulls the palatoquaxlrate back into place, its 

 action thus being largely, if not entirely, to pull the palatoquad- 

 rate dorso-mesially in the plane of the apparatus. The articular 

 attachment of the processus metaptei-ygoideus to the postorbital 

 process, in Heptanchxis and Hexanchus, would evidently have to 

 be somewhat loose to permit of this motion, and Luther (1909) 

 assumes that there is here a certain dorso-ventral sliding motion, 

 and, also, that the levator muscle must act in part as an adductor 

 palatoquadrati. Furthermore, the attachment of the palato- 

 quadrate to the hyomandibula must be such as to allow a certain 

 amount of motion between them. 



In certain others of the Plagiostomi this metapterygoid ridge 

 of the Kotidanidse has become a pronounced process, and both 

 Gegenbaur (1872) and Luther (1909) have called it a muscle 

 process. It apparently lies directly upon the dorso-mesial edge 

 of the palatoquadrate, thus having in the adults of these fishes 

 the position that it has in larvae of Amia. Where present it has 

 the same relations to the levator and adductor muscles that the 

 ridge-like process of the ISTotidanidse has, and because of its 

 articular relations to the cranial wall, in the latter fishes, it has 



