91] THE SKULL OF AM lURUS— KINDRED 91 



the substance of the basioccipital than they do in other teleost groups, but the 

 saccuH always have a relation to the dorsal surface of the bone. The inter- 

 digitation of basioccipital with parasphenoid, and articulations with prootic 

 and exoccipital, are common characters. The processes on the bone for 

 articulation with the transscapular process are peculiar to the Siluridae. The 

 pharyngeal processes of the Characinidae and Cyprinidae, extending from the 

 ventral surface of the basioccipital to the wall of the swim-bladder, are not 

 found in other teleosts. Allis (1910) mentions a groove on the dorsal surface 

 of the basioccipital in the Loricati, which he claims as the homologue of the 

 cavum sinus imparls of the Ostariophysi. The basioccipital throughout the 

 teleosts is usually excluded from participation in the formation of the foramen 

 magnum by the union of the posterior ends of the exoccipitals above it or by 

 the presence of the sinus impar. 



The bulk of the bone is developed from the posterior parachordalia and the 

 ossification of the intercranial notochord. In some of the Cyprinidae con- 

 siderable cartilage remains in those parts of the bone which form the walls 

 and floor of the recessus sacculorum. In all of the teleosts, the notochord 

 disappears in that part of the basioccipital anterior to the vertebral articular 

 smiace. In the forms with an eye-muscle canal, the basioccipital forms its 

 posterior floor. 



The premaxillaries are a pair of bones forming the anterior end of the upper 

 ja^ and are closely fused with each other in the mid- ventral line of the cranimn. 

 They have no ascending process, such as occurs in Salmo, Scomber, Alepo- 

 cephalus and other teleosts, but are closely fused to the ventral surface of the 

 supraethmoid bone. They curve posteriorly on each side to form the osseous 

 floor of the nasal fossae and are attached by ligament to the palatine and 

 maxillary bones dorso-posteriorly. The ventral surface of each bone is covered 

 with teeth, which, as mentioned in the younger stage are only secondarily 

 connected with it (Fig. 15). 



The maxiUaries. Each maxillary bone (Fig. 15) lies latero-posterior to the 

 premaxillary, embedded in the connective tissue forming the lateral margins 

 of the upper lips. Each is toothless and serves as a support for the elongate 

 laterally extending, maxillary barbel. This lateral position of the maxillary 

 is common among the teleosts and occurs in Amia also. In Salmo, the bone is 

 continuous posteriorly with the premaxillary and bears a series of teeth on its 

 ventral surface. In Scomber it lies partly internal to the premaxillary and 

 has an articular surface for it. In the Loricati the bone has a long posterior 

 extent and overlaps the mandible. In none of these forms is it as small as in 

 Amiurus where it has a slender styhform shape and is held in position partly 

 by connective tissue. It is in actual contact with the palatine bone, articulat- 

 ing with it by means of a small ball and socket joint, the latter lying on the 

 palatine. 



