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, "Jii; of 

 Amniota, 726 



Urinogenital organs, see 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 



Vasa efferentia, of Elasmobranchs, 697 ; 

 of Amphibia, 711; general origin of, 

 724 



Vascular system, of Amphioxus, 8; Petro- 

 myzon, 97; Lepidosteus, 116; general 

 development of, 632 



Vas deferens, of Elasmobranchii, 697 ; 

 of Amniota, 723 



Vein, sub-intestinal of Petromyzon, 97 ; 

 Acipenser, no; Lepidosteus, 116 



Velum of Petromyzon, 9 1 



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, 175 



Vertebral bodies, of Chick, 183 



Vertebral column, development of, 545, 

 549; epichordal and perichordal de- 

 velopment of in Amphibia, 556 



Vespertilionidse, early development of, 

 217 



Vieussens, valve of, 426 



Villi, placental, of zona radiata, 235 ; 

 subzonal membrane, 235; chorion, 237; 



Man, 246; comparative account of, 

 2 575 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; prseoral, 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, 109; 

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

 fluence of on formation of layers, 278; 

 influence of on early development, 



341, 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, 81; enclosure 

 of, 75 ; circulation of, 81 



Zona radiata, villi of, 237 

 Zonula of Zinn, 495 



