DEVELOPMENT OF THE KEPKODUCTIVE OKGANS. 



887 



m 



3. The pancreas arises in the same way as the salivary glands, but is not visible at the 4th 

 week (His). 



4. The liver begins very early, and appears as a diverticulum, with two hollow primitive Jiepatic 

 ducts, which branch and form j 

 bile-ducts. At their periphery * 

 they penetrate between the solid 

 masses of cells the liver-cells 

 which are derived from the hypo- 

 blast. At the 2nd month the 

 liver is a large organ, and secretes 

 at the 3rd month ( 182). 



5. In birds two small blind 

 sacs are formed from the hind-gut. 



6. The foetal respiratory organ, 

 the allantois, is treated of speci- 

 ally ( 444). 



Peritoneum and Mesentery. 

 The inner surface of the ccelom, 

 or body-cavity, the surface of the 

 intestine, and its mesentery are 

 covered by a serous coat the 

 peritoneum. At first the simple 

 intestine is contained in a fold, 

 or duplicature of the peritoneum ; 

 on the stomach, which is merely 

 at first a spindle-shaped dilata- 

 tion of the tube placed vertically, 

 it is called mesogastrium. After- 

 wards, the stomach turns on its 

 side, so that the left surface "is 

 directed forwards and the right 

 backwards. Thus, the insertion 

 of the mesogastrium, which ori- 

 ginally was directed backwards (to 

 the vertebral column), is directed to the left ; the line of insertion forming the region of the 



Fig. 681. 

 Formation of the omentum. I and II. hg, gastro-hepatic 

 ligament ; m, great, n, lesser curvature of the stomach ; 

 s, posterior, and i, anterior fold or plate of the omentum ; 

 mc, mesocolon; c, colon. III. X, liver; t, small intes- 

 tine ; b y mesentery ; p, pancreas ; d, duodenum ; r, rectum ; 

 i\T, great omentum. 



&/J (M 



Fig. 682. - 



Development of the internal generative organs. I. , Undifferentiated condition D, reproductive 

 gland, lying on the tubules of the Wolffian body ; W, Wolffian duct ; M, Mullerian duct ; 

 S, uro-genital sinus. II., Transformations in the female F, fimbria, with the hydatid, 

 h 1 ; T, Fallopian tube ; U, uterus ; S, uro-genital sinus ; 0, ovary ; P, parovarium. III., 

 Transformations in the male H, testis ; E, epididymis, with the hydatid, h ; a, vas 

 aberrans ; V, vas deferens ; S, uro-genital sinus ; u, male uterus. 4, d, hind-gut ; a, 

 allantois ; w, urachus ; K, cloaca. 5, M, rectum ; m, perineum ; b, position of the bladder; 

 S, uro-genital sinus. 



great curvature, which becomes still more curved. From the great curvature, the mesogastrium 

 becomes elongated like a pouch (fig. 681, I and II, s, i), constituting the omental sac, which 



