88 



COMPARATIVE ANATOMY. 



FIG. 69. PECTORAL ARCH AND FIN OF Heptanchus. 



/S'.Z>', /S',2? 1 , pectoral arch, with a nerve-aperture at NL ; Pr, Ms, Mt, the three 

 basal elements of the fin pro-, meso-, and metapterygium ; lia, cartilaginous 

 fin-rays ; a,, b, the main fin-ray, lying in the axis of the metapterygium ; 

 t, single ray on the other side of the axis (indication of a biserial type) ; FS, 

 horny rays, cut through. 



Cm 



Co(Cl) 



FIG. 70. LEFT PECTORAL ARCH AND FIN OF THE TROUT. (From the outer side.) 

 D, JJ 1 , D 2 , chain of secondary bones of the pectoral arch (clavicle and supraclavicle), 

 which is connected with the bkull by means of the post-temporal (Cm) ; S and 

 Co(Cl), bony scapula and coracoid, which have become developed in the cartiliigc. 

 (Kri) ; L, foramen in scapula ; If 1 , metapterygium ; En, lia, the second and 

 third, and 4, the fourth basal element of the fin ; Ha 1 , the second cartilaginous 

 row of radii ; US, bony ray on the border of the fin, which is connected with the 

 fourth basal element ; F, S, bony fin-rays, shown cut away from their attachments. 



