140 ZOOLOGY SECT. 



and Meckel's cartilage. The lower lateral cartilage is the cerato- 

 liyal (cer. hi/.). Both the hyo-mandibular and cerato-hyal bear a 

 number of slender cartilaginous rods the branchial rays of the 

 hyoid arch. The mesial element, or basi-hyal (b. hy.\ lies in 

 the floor of the pharynx. Behind the hyoid arch follow the 

 branchial arches, which are five in number. Each branchial arch, 

 with exceptions to be presently noted, consists of four cartilages. 

 The uppermost of these pharyngo-branchial (ph. br. l -ph. br. 5 ) lie 

 in the dorsal wall of the pharynx, not far from the spinal column ; 

 the pharyngo-branchials of the last two arches are fused together. 

 The next in order the epibranchials (ep. br.) with the exception 

 of those of the last arch, bear a number of slender cartilaginous 

 rods the branchial rays which support the walls of the gill-sacs ; 

 and the next the cerato-branchials (cer. br.) are, with the same 

 exception, similarly provided. The hypo-branchials (hyp. br.), which 

 succeed these, are absent in the case of the first and fifth arches. 

 In the middle line on the floor of the pharyngeal cavity is a mesial 

 cartilage the basi-branchial (Fig. 769, b. br.) which is connected 

 with the ventral ends of the third, fourth, and fifth arches. Three 

 pairs of slender curved rods the extra-branchials lie superficial 

 to the second, third, and fourth branchial arches, along the borders 

 of the corresponding branchial clefts. 



Two pairs of delicate labial cartilages lie at the sides of the 

 mouth, and a couple at the margins of the openings of the olfactory 

 capsules. 



The skeleton of all the fins paired and unpaired presents a 

 considerable degree of uniformity. The main part of the expanse 

 of the fin is supported by a series of flattened segmented rods, the 

 pterygiophores or cartilaginous fin rays, which lie in close apposition : 

 in the case of the dorsal fins these are calcified along their axes. At 

 the outer ends of these are one or more rows of polygonal plates of 

 cartilage. On e#ch side of the rays and polygonal cartilages are a 

 number of slender horny fibres of dermal origin. In the smaller 

 median fins there may be an elongated rod of cartilage constituting 

 the skeleton, or cartilage may be entirely absent. In the pectoral fin 

 (Fig. 770) the fin rays are supported on three basal cartilages articu- 

 lating with the pectoral arch. The latter (pect.) is a strong hoop 

 of cartilage incomplete dorsally, situated immediately behind the 

 last of the branchial arches. It consists of a dorsal, or scapular, 

 and a ventral, or coracoid portion, the coracoid portions of oppo- 

 site sides being completely continuous across the middle line, 

 while the scapular are separated by a wide gap in which the 

 spinal column lies. Between the two portions are the three arti- 

 cular surfaces for the three basal cartilages. The coracoid portions 

 are produced forwards in the middle line into a flattened process 

 supporting the floor of the pericardial cavity in which the heart 

 is lodged. The three basal cartilages of the fin are named, 



