SKULL — CHONDROCRANIUM 



67 



and may fuse in the median line or may be connected only by 

 ligament. It is said that sometimes a copula exists between the 

 anterior ends of the Meckelian, strengthening its resemblance to the 

 other arches. Pterygoquadrate and Meckel's cartilage articulate 

 behind, forming the hinge of the jaws. 



Fig. 71. — Visceral arches of Acanthias (Wells', '17). bh, basihyal; cb, ceratobran- 

 chial; ch, ceratohyoid; eb, epibranchials; hm, hyomandibula; m, Meckel's cartilage; 

 phb, pharyngobranchials; pq, pterygoquadrate. 



This is a good place to mention the ways in which the jaws are 

 connected with the cranium. Several authors have discussed the 

 different methods of suspension, but possibly the best grouping is 

 that of Gregory ('04). Holostyly is characterized by a primitive 



Fig. 72. — Skull of Squatina (Gegenbaur). h, hyoi(»; hm, hyomandibula; hr, 

 hyomandibular rays; /, labial cartilages; m, Meckel's cartilage; pq, pterygoquadrate; 

 r, rostrum. 



hyoid arch which plays no part in suspension of the jaws, while the 

 pterygoquadrate bar, at first separate from the cranium (fig. 66), 

 fuses with it later so that no line of separation occurs in the adult. 

 This condition is known only in Holocephals (fig. 91). In the 



