922 



EMBRYOLOGY. 



itself from this germ, and passing backward to serve, at a later period, in 

 forming tlie persistent tooth. 



3. The liver. — This gland commences to be developed very early in all 

 the species. It appears on the surface of the duodenum in the form of two 

 or more buds, according to the number of lobules in the adult liver. To 



these external buds are correspond- 

 Fig. 448. ijig internal ones, arising from the 



intestinal epithelium. The first 

 enlarge and envelope the omphalo- 

 mesenteric vein ; the second ramify 

 in their interior, and form the 

 system of biliary canals. 



The liver grows rapidly, and, 

 towards the third month, almost 

 entirely fills the abdominal cavity ; 

 at a later period its growth is less 

 opjaiN OF THE LivEE PKOM THE INTESTINAL marked,^ although at birth it is yet' 

 WALL IN THE EMBRyo OP THE FOWL, ON THE proportionally larger than in adult 



FOURTH DAT OP INCUBATION. h£e. 



a, Heart ; 6, Intestine ;c, Everted portion, giving 4. Pancreas. — The pancreas 



origin to liver ;cf, Liver; ..Portion of vitel- fij,gt i^Jj-q ^he Salivary 



iiDG vesicle. _- • i-\ t* (* 1**1 



glands, m the torm ot a solid 

 cellular bud, which afterwards is channeled into ramescent cavities. 



5. Spleen. — According to Bischoff, this body is developed, during the 



second month, on the large curvature of the stomach. Arnold states that it 



is formed at the same time as the liver, in a strip extending from the 



stomach to the duodenum. It subsequently separates from the pancreas and 



becomes fixed to the stomach, where its elements 



Fig. 449. assume the character of spleen tissue. 



DEVELOPMENT OF THE GENITO-TTEINAET APPARATUS. 



The development of the genital is related to that 

 of the urinary organs, as the apparatus they form 

 have some parts in common. 



Immediately after the formation of the intes- 

 tines, the genito-urinary organs are supplied by the 

 Wolffian bodies. These, also named the primordial 

 hidneys and lodies of Olcen, are glandular in structure, 

 and extend in front of the vertebral column from the 

 heart to the pelvis. They are composed of small 

 transverse canals, filled with a whitish fluid, which 

 enter a common excretory duct that lies parallel to 

 the spine, and opens inferiorly into that portion of 

 the allantois that becomes the bladder. The Wolf- 

 uEiNAET APPAEATus IN fiau bodies are placed behind the peritoneum, and 

 THE b^d"^ ^*'™™ °^ ^';® attached by two serous folds : an anterior, the 

 diaphragmatic ligament, and a posterior, the lumbar 

 ligament of the corpora Wolffiana. The organs furnish 

 a liquid analogous to the urine; though it is not 

 long before their secretion imdergoes great modi- 

 fications ; indeed, these bodies soon atrophy, and dis- 

 appear more or less rapidly, according to species. One portion serves for 



i-m 



STATE OF THE GENITO- 



:, Corpora Wolffiana ; b, h, 

 Their excretory ducts; 

 c, Kidneys; d, Ureter; 

 e, e. Testes. 



