922 



.EMBRYOLOGY. 



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

 forming the 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. n g 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 

 ORIGIN OF THE LIVER FROM THE INTESTINAL marked, although at birth it is yet 

 WALL IN THE EMBRYO OF THE FOWL, ON THE proportionally larger than in adult 



FOURTH DAY OF INCUBATION. 



a, Heart ; 6, Intestine ; c, Everted portion, giving 



4 Pancreas. The 

 a PP ear > like the. 



pancreas 

 salivary 



glands, in the form of 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-UKINARY 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 

 Wolman bodies. These, also named the primordial 

 kidneys and bodies of Oken, 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 

 STATE OF THE GENITO- the allantois that becomes the bladder. The Wolf- 

 FRINARY APPARATUS IN fian bodies are placed behind the peritoneum, and 



THE Bmo Y EMBRY F are attache( * b 7 two seroils folds : an anterior, the 

 diaphragmatic liqamenL and a posterior, the lumbar 



, Corpora Wolffiana ; 6, b. 7 . * ^ . ,, J L- r 7/r , rm j? i, 



Their excretory ducts ; %wen< of the corpora Wolffiana. The organs furnish 



c, Kidneys; d, Ureter; a liquid analogous to the urine; though it is not 



e, #, Tetes. long before their secretion undergoes great modi- 



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



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



