93] THE SKULL OF AM I URUS— KINDRED 93 



In Megalops (Ridewood, 1904), a large ectopterygoid hinders its anterior 

 extent and it overlaps the hyomandibular posteriorly. In Pleuronectes (Cole 

 and Johnson, 1901), it is smaller than in Amiurus and lies posterior and dorsal 

 to the quadrate. The small metapterygoid of the Characinidae is separated 

 from the ectopterygoid and quadrate by cartilage and there is also a large 

 foramen between it and the latter. 



The quadrate. This bone is situated at the ventro-anterior end of the 

 hyomandibular suspensorial apparatus (Fig. 15). It is grooved on its inferior 

 face for articulation with the mandible. It is rather small, and firmly fused 

 to the surrounding bones, although there is a small area between it and the 

 hyomandibular, where the underlying persisting cartilage shows between the 

 bones. Its posterior face interdigitates with the preopercular bone. Mc- 

 Murrich (1884) states that the cartilage mentioned as occurring between the 

 bones is the symplectic and that in perfectly dried skulls there is a space 

 between the hyomandibular and the quadrate due to the absence of cartilage. 



The hyomandibular. This large bone connects the quadrate with the 

 cranium. It is immovably fused with the latter and if one moves, both must. 

 A process of the bone projects from the anterior edge to the lateral surface of 

 the aHsphenoid' which is hollowed out for its reception. Posterior and dorsal 

 to this point of contact the hyomandibular articulates with the side of the 

 craniiun in a groove which has been described in connexion with the sphenotic 

 and squamoso-pterotic bones. There are several ridges on the lateral surface 

 of the bone along which the adductor muscles are attached (Fig. 15). Just 

 above its interdigitation with the preopercular is a foramen for the passage of 

 the ramus hyomandibularis facialis. The knob for tlie articulation of the 

 operculum has ossified and is overlapped by the ventral surface of this bone, 

 which is hollowed out as a socket for movement on the knob. 



In Salmo (Parker, 1873), the hyomandibular does not have the anterior and 

 ventral extent that it has in Amiurus and it is isolated from the surrounding 

 bones by cartilage. Parker does not figure the foramen for the hyomandibu- 

 laris nerve, but from Gaupp's figure (1906) of the foramen in the younger stage of 

 Salmo, it is evident that the nerve passes farther forward than in Amiurus. 

 In the Albulidae and Mormyridae, and other lower teleosts, the hyomandibular 

 does not have so great an anterior, posterior, or ventral extent as in Amiurus, 

 and usually a small symplectic element comes between it and the quadrate. 

 The preopercular does not articulate with the hyomandibular as closely as in 

 Amiurus. In all of the teleosts the hyomandibular has a knob on its posterior 

 edge for the articulation of the operculum; in some of the Characinidae carti- 

 lage persists at this point. 



The dentary. The teeth which are borne on the lower jaw are attached to 

 the medial dorsal surface of this bone, from the symphysis as far back as the 

 dentary-articulare interdigitation. The bone retains the shape and relations 



