SKULL — -TELEOSTOMES 



91 



vertebrates and an advance beyond the purely cartilage skull of Elasmobranchs. 

 A few figures with the usual nomenclature of parts are as good as any detailed 

 description for present purposes. Ostracoderms are often distributed into 

 groups of Heterostraci, Osteostraci and Antiarcha; the relations of all to other 

 Vertebrates being very uncertain. 



TELEOSTOMI are normal tishes, higher than Elasmobranchs, in 

 which membrane bones, and to a greater or less extent, cartilage 

 bones have developed in the skull. The Chondrostei, except for 



Fig. 96. — Dorsal and side views of Amiurus chondrocranium (Kindred, '19). 

 c, ethmoid cornu; ca, notch for carotid; e, ethmoid plate; eb, epiphysial bar; hm, hyo- 

 mandibula with foramen for hyomandibular nerve; hy, hyale; ih, interhyal region; 

 m, Meckel's cartilage; oa, occipital arch; oc, otic capsule; op, opercular process; pa, 

 'palatine' cartilage; pc, parachordal; pq, pterygoquadrate; /, trabecula. 



bones, have hardly passed the sharks, and the following general 

 statement omits them, discussion of their features being given later. 

 Except for a few (mostly lower) forms, little is known of the develop- 

 ment of the skull and the homologies of several of the bones are 

 uncertain. To a greater extent than elsewhere, certain bones have 

 a double origin, being formed by an intimate union of a cartilage bone 

 with an overlying bone, clearly of dermal origin, as occurs in the 



