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downward, outward, and backward; (2) the cerato-hyal cartilage, 

 which is movably articulated to the hyomandibular and extends 

 downward, forward and inward. The ventral ends of the ceratohyals 

 are united by a median, plate-like basihyal. 



The palato-quadrate and Meckelian cartilages are suspended 

 from the hyomandibular by several strong ligaments, the direct at- 

 tachments of the jaws to the cranium being of soft connective tissue 

 only. Both the hyomandibular and ceratohyal cartilages bear slen- 

 der rods (branchial rays} on their posterior edges, which support 

 the anterior wall of the first gill-pouch. Note the position of the 

 spiracle between the mandibular and hyoid arches. The anterior 

 wall of the spiracle is strengthened by two small, flat, vertical car- 

 tilages, probably homologous with the branchial rays of the gill- 

 arches. 



The remaining five visceral arches differ little in their construc- 

 tion. Dorsally, each has a flat, sickle-shaped pharyngo-branchial 

 cartilage attached to the vertebral column by fibrous bands. The 

 pharyngobranchials of the last two arches are fused. Ventrad to 

 each pharyngobranchial is an epibranchial cartilage. The next 

 segment of each arch is formed by the ceratobranchial cartilage. All 

 the epibranchials and ceratobranchials except those of the fifth 

 arch bear slender branchial rays. The ventral ends of the cerato- 

 branchials articulate with each other, the first being attached to the 

 ceratohyal by ligament. The second, third, and fourth arches have 

 another more ventral series of cartilages, the hypobranchials. The 

 lower ends of the hypobranchials are attached to a large median 

 plate, the basibranchial. The fourth ceratobranchial joins the third 

 hypobranchial, while the ceratobranchials of the fifth arch are at- 

 tached to the basibranchial directly. The basibranchial is com- 

 posed of two segments closely united by ligament; the anterior one 

 narrow, the posterior broad and flat in front, tapering to a sharp 

 point behind. 



Short teeth of cartilage, called gill rakers, project into the 

 pharynx from the inner edges of the arches. 



A dorsal and a ventral series of extra-branchial cartilages, thin, 

 slender plates, lie on the external side of each gill-arch. 



PECTORAL GIRDLE AND FIN. Remove from the body the pectoral 

 girdle, with the fins attached, and carefully scrape off the muscles 

 from the cartilaginous parts. It will be found that the support of 

 the fin is partly of cartilaginous plates and rods, partly of horny 

 fibres (dermal fin-rays) which overlie the extremities of the car- 

 tilages and extend to the edges of the fin. These fibres are in two 

 layers, one beneath the skin of each side. They are formed in the 

 derniis. A similar arrangement of horny fibres is found in all the 

 other fins. 



The pectoral girdle passes across the ventral surface of the body 

 and upward on each side to the level of the vertebral column. The 

 stout ventral bar presents numerous facets for the origin and inser- 

 tion of muscles. The articular surfaces for the pectoral fins are 

 well up on the sides of the girdle. The slender dorsal end of each 

 side of the girdle consists of a separate bar of cartilage, movably 

 articulated to the lower portion. The ascending limb of the girdle, 

 from the fin articulations to the base of the cartilage just mentioned, 

 is called the scapular portion; the small bar is the supra-scapular; 

 the ventral bar between the fin articulations is the coracoid portion. 



The cartilaginous skeleton of the pectoral fin consists primarily 

 of a row of three basal cartilages, all articulating proximally with 

 the girdle. The middle basal is much the largest. Distal to the 



