792 



INDEX. 



Tympanohyal, 591 



Umbilical canal of Elasmobranchii, 54, 



57, 58, 59 



Umbilical cord, 238; vessels of, 239 

 Ungulata, placenta of, 250 

 Urachus, 239, 726 

 Ureters, of Elasmobranchii, 696; develop- 



ment of, 723 

 Urethra, 727 

 Urinary bladder of Amphibia, 712; of 



Amniota, 726 

 Urinogenital organs, sec Excretory or- 



gans 

 Urinogenital sinus of Petromyzon, 700; 



of Sauropsida, 726; of Mammalia, 



727 



Urochorda, development of, 9 

 Uterus, development of, 726; of Marsu- 



pials, 726 



Uterus masculinus, 726 

 Utriculus, 519 

 Uvea of iris, 489 



Vagus nerve, development of, 456, 457; 



intestinal branch of, 458; branch of to 



lateral line, 459 

 Valve, spiral, of Petromyzon, 97; Aci- 



penser, no; general account of, 767 

 Valves, semilunar, 641; auriculo-ventri- 



cular, 642 

 Yasa efferentia, of Elasmobranchs, 697 ; 



of Amphibia, 711; general origin of, 



Vascular system, of Amphioxus, 8 ; Petro- 



myzon, 97; Lepidosteus, 116; general 



development of, 632 

 \ "as deferens, of Elasmobranchii, 697; 



of Amniota, 723 

 Vein, sub-intestinal of Petromyzon, 97 ; 



Acipenser, no; Lepidosteus, 116 

 Velum of Petromyzon, 91 

 Vena cava inferior, development of, 655 

 Venous system of Petromyzon, 97; gene- 



ral development of, 651 ; of Fishes, 



651 ; of Amphibia and Amniota, 655 ; 



of Reptilia, 656; of Ophidia, 656; of 



Aves, 658; of Mammalia, 661 

 Ventricle, fourth, of Chick, 176; history 



of, 424 



Ventricle, lateral, 438, 440; fifth, 443 

 Ventricle, third, of Chick, 171; 

 Vertebral bodies, of Chick, 183 

 Vertebral column, development of, 545, 



549; epichordal and perichordal de- 



velopment of in Amphibia, 556 

 Vespertilionidce, early development of, 



217 



Vieussens, valve of, 426 

 Yilli, placenta!, of zona radiata, 235 ; 



subzonal membrane, 235; chorion, 237; 



Man, 246 ; comparative account of, 

 257; of young human ovum, 265, 269 



Visceral arches, Amphioxus, 7 ; Elasmo- 

 branchii, 57 60; Teleostei, 77; Aci- 

 penser, 1 06; Lepidosteus, 116; Am- 

 phibia, 133; Chick, 177; Rabbit, 

 231 ; pneoral, 570; relation of to head 

 cavities, 572; disappearance of pos- 

 terior, 573; dental plates of in Teleo- 

 stei, 574 



Visual organs, evolution of, 470 



Vitelline arteries of Chick, 195 



Vitelline veins of Chick, 195 



Vitreous humour, of Ammoccetes, 98 ; 

 general development of, 494; blood, 

 vessels of in Mammals, 503 ; meso- 

 blastic ingrowth in Mammals, 503 



Vomer, 594 



White matter, of spinal cord, 415; of 

 brain, 423 



Wolffian body, see ' Mesonephros ' 



Wolffian duct, first appearance of in 

 Chick, 183; general account of, 690; 

 of Elasmobranchs, 693 ; of Ganoids, 

 704; of Amphibia, 710; of Amniota, 

 713; atrophy of in Amniota, 724 



Wolffian ridge, 185 



Yolk blastopore, of Elasmobranchii, 64 



Yolk, folding off of embryo from, in 

 Elasmobranchii, 55 ; in Teleostei, 76 ; 

 Acipenser, 106; Chick, 168, 170 



Yolk nuclei, of Elasmobranchii, 41, 53; 

 Teleostei, 69, 75 



Yolk, of Elasmobranchii, 40; Teleostei, 

 68 ; Petromyzon, 96 ; Acipenser, 1 09 ; 

 Amphibia, 122, 129; Chick, 146; in- 

 fluence of on formation of layers, 278; 

 influence of on early development, 



34 r > 342 



Yolk-sack, Amphibia, 131, 140, 141; en- 

 closure of, 123 



Yolk-sack, development of in Rabbit, 

 227; of Mammalia reduced, 227; cir- 

 culation of in Rabbit, 233; enclosure 

 of in Sauropsida, 289 



Yolk-sack, enclosure of, Petromyzon, 86 



Yolk-sack, Lepidosteus, 118 



Yolk-sack of Chick, enclosure of, 160; 

 stalk of, 174; general account of, 193; 

 circulation of, 195 ; later history of, 198 



Yolk-sack of Elasmobranchii, enclosure 

 of, 62, 283; circulation of, 64 



Yolk-sack of Lacerta, 209 ; circulation of, 

 209 



Yolk-sack, Teleostei, 75, Si ; enclosure 

 of, 75; circulation of, 81 



Zona radiata, villi of, 237 

 Zonula of Zinn, 495 



