220 THE FEMALE REPRODUCTIVE SYSTEM 



rectum and a ventral urogenital vestibule before birth. In these 

 forms the Miillerian ducts fuse into a single passageway whose 

 anterior portion forms the vagina, which opens into the vestibule 

 separately from the urethra. 



The oviducts show modifications depending upon the type of 

 egg and its future development. In the case of the large, shelled 

 eggs of birds and reptiles, there are specialized portions of the ducts 

 which secrete the additional material. In the placentals, the egg 

 is fertilized in the upper portion of the oviduct and then conducted 

 to a lower portion, the uterus, which is modified for implantation 

 and internal development of the embryo. 



In general, the oviducts have ciliated columnar epithelium lining 

 the lumen. Simple tubular glands of varying prominence, depend- 

 ing on the season, extend into the subepithelial fibroelastic connec- 

 tive tissue. Loose fibroelastic connective tissue of the submucosa 

 forms folds projecting the mucosa into the lumen. Below the sub- 

 mucosa there is usually a broad coat of circular smooth muscle 

 separated from a less prominent outer longitudinal coat by a region 

 of vascular fibroelastic connective tissue. In the lower regions of 

 the oviducts, compound tubular glands may form relati\ely large 

 evaginations of the mucosa, as in the skate, composing the shell 

 glands whose secretions are carried into the lumen by numerous 

 excretory ducts lined with mucous columnar cells. 



Amphibia. Amphibian oviducts consist of a pair of long, con- 

 torted tubes, each connected with the wall of the body ca\ity in 

 the dorso-lateral region by a mesenteric sheet. Anteriorly, each 

 opens by a ciliated funnel-shaped ostium into the body cavity; 

 posteriorly they connect with the dorsal wall of the cloaca near the 

 entrance of the ureters. In immature animals and between breeding 

 seasons the oviducts are small, thin-walled structures, but during 

 breeding season there is a great increase in size and they become 

 more convoluted. Over the greater part of its length each duct is 

 of uniform size, but near the cloaca there is a dilated region. The 

 entire duct has an outer adventitia of connective tissue covered by 

 peritoneum. A thin nniscularis of circular smooth muscle cells 

 adjoins the adventitia and is difficult to distinguish where the 

 glandular mucosa forms the greater portion of the wall. The 

 lumen is lined by ciliated columnar cells with goblet cells inter- 

 spersed. Over the greater length of the duct, the nuicosa is com- 

 posed of long tubular glands. These glands secrete the albumen 

 surrounding the eggs as they pass down the o\iducts. At the dilated 



