330 



THE ELASMOBRANCH FISHES 



Semicircular canal, 55, 258, 271, 273; am- 

 pullae of, 259, 273; anterior oblique, 

 43, 258, 273; development of, 275; 

 nerves to, 261, 273; posterior oblique, 

 43, 259, 273 



Seminal vesicle, 302 



Sense of smell, 265 



Sensory canal system, 261-263; canals of, 

 261-262; function of, 279; nerves to, 

 262; neuromasts of, 262, 278; of Elas- 

 mobranchs in general, 274-279; of 

 Heptanchus, 261-263; structure of, 278 



Sensory fibers, 238; origin, 238 



Sensory (dorsal) root nerve, 246 



Septum, constricting notochord, 48; of 

 gill, 147, 148, 149 



Serosa, 170 



Serum, 170 



Sex cells, 301, 302, 303; passage of, to 

 cloaca of female, 310; passage of, to 

 clasper of male, 303; sex gland, 300 



Sex characters (secondary), 309; claspers, 

 309 



Shagreen denticles, 7, 23 



Sharks: angel fish (Squatma) , 9, fig. 18; 

 ancient, 1; basking, 3; blue, 3; flattened, 

 3 ; generalized, 2 ; hammerhead, 2 ; hep- 

 tanchid, 5-7, figs. 12, 13, 14; heterodont, 

 1, fig. 17; lamnoid, 9; man-eater, 2, 9, 

 fig. 16; modern or recent, 2, 3; preda- 

 cious, 9; specialized, 2; swell, 2, fig. 1; 

 thresher, 2, fig. 2 



Shell gland, 290, 304-305; secretory cells 

 of, 305 



Sinu-auricular aperture, 171 



Sinu-auricular valve, 160, 171 



Sinus, 204 



Sinus of photophore, 29 



Sinus venosus, 160, 170, 171; tributaries 

 to, 201, 211, 215 



Siphon, 28, 303; function of, 303; relation 

 of, to clasper tube, 303 



Skeleton, 43-52, 53-83; development of, 

 77-79; nature of, 53; in anal fin, 52, 83; 

 of caudal fin, 51; of clasper, 51, 81-82; 

 of dorsal fin, 51, 82-83; of pectoral fin, 

 49, 75-79; of pelvic fin, 51, 81-82; of 

 paired fins, 50-51, 75-82; of unpaired 

 fins, 51, 82-83 



Skin. See Integument 



Skull, 43-47, 53-69; components of, 43, 

 53 



Somatic layer, 96 



Somatic sensory fibers; terminus of, 236 



Somite, 70, 96; degeneration of, 97; of 

 head, 99-100; parts of, 96 



Special senses, of Elasmobranchs in gen- 

 eral, 264-282; of Heptanchus, 258-263. 

 See also Organs of special sense 



Si^erm sac, 302 



Spermatagonia, 301 



Spermatic fluid, 302 



Spermatid, 301 



Spermatozoa, 291, 301, 302 ; course of, to 

 female, 309 



Spinal artery, 186 



Spinal column, 47, 69; calcification in,74- 

 75; in Elasmobranchs in general, 69- 

 75; in Heptanchus, 47-48; relation of, 

 to notochord, 70 



Spinal cord, 222, 237-238; arteries to, 

 169, 192, 193; development of, 230, 237; 

 in Elasmobranchs in general, 237—238; 

 in Heptanchus, 222 



Spinal nerves, 227, 246; in Elasmobranchs 

 in general, 246-247; roots of, 227, 237, 

 246 



Spinalis artery, 186 



Spinax, color in, 27; photophores of, 29 



Spiracle, absence of, 150; blood supply 

 to, 181-182; diverticula of, 147-148, 

 153; filaments of, 147, 153; in rays, 

 150; relation of, to gill clefts, 150 



Spiracular ampulla, 280 



Spiracular cartilage, 63, 153 



Spiracular diverticulum. See Diverticula 

 of spiracle 



Spiracular valve, 153; muscles of, 153- 

 154; support of, 153 



Spiral intestine, 139-140; mesentery to, 

 121 



Spiral valve, 124, 126, 139; arteries to, 

 167; development of, 140; extent of, 

 126, 139-140; function of, 140; lining 

 of, 126, 140 ; turns of, 124, 140 ; veins of, 

 210-211 



Splanchinie layer, 96 



Spleen, arteries to, 166, 167, 188; in Hep- 

 tanchus, 124, 138; position of, 138-139 



Spouting, 156-157; course of, 156-157; in 

 Squat ina, 156-157 



Squalii^ sucMii, gill rakers of, 37 ; relations 

 of subscapular vein of, 214 



Squatina, 9, fig. 18; clasper gland of, 28; 

 spouting in, 156-157 



Stapedeal artery. See Orbital artery 



Sting, 35, 37; function of, 37; glands of, 

 28; structure of, 37 



