324 AN INTRODUCTION TO ZOOLOGY 



uteri open by separate projecting apertures, the ossa uteri, into the 

 succeeding portion of the genital tract, the vagina, which is a median 

 unpaired structure representing the fused distal ends of the old 

 pronephric ducts. Uteri and Fallopian tubes are attached to the 

 dorsal wall of the abdominal cavity and held in place by a stout fold 

 of peritoneum, termed the broad ligament. The vagina passes 

 backwards to open into the neck of the bladder, so that from this 

 point on, as in the male, we have a common urogenital duct here 

 termed the vestibule. Its walls are very vascular, corresponding to 

 the corpus spongiosum of the male. In the anterior median wall 

 is a small rod-like body, the clitoris, corresponding with the penis in 

 the male, and terminating externally in a soft sensitive spot, the 

 glans clitoridis. Internally two small corpora spongiosa pass back 

 from it to bifurcate in the abdominal wall and become attached to 

 the ischia. The actual external opening is termed the vulva, and it is 

 guarded by two lips. No glands corresponding to the prostate of 

 the male are present, but Cowper's glands are represented by two 

 areas containing the small glands of Bartholini. Perineal and rectal 

 glands are present as in the male, and the urogenital tract is similarly 

 related to the rectum. 



Ductless Glands. 



Before passing on to consider the nervous system it will 

 be as well to glance quite briefly at the ductless glands. As in the 

 frog, we shall include under this heading not only the glands in the 

 strict sense of the term, but also the lymphoid organs. 



The Spleen. This is a dark red elongated body attached to the 

 dorsal side of the cardiac end of the stomach by a side fold of the 

 mesentery, the gastro-splenic omentum. It is the largest of the 

 haemolymph organs, and is enclosed in a quite distinct capsule 

 composed of a mixture of fibrous and non-striate muscular tissue. 

 From this capsule strands of tissue, the trabeculse, pass inwards to 

 ramify through the mass of the organ which is mainly composed of a 

 soft tissue termed the splenic pulp, which contains several varieties 

 of characteristically shaped cells. It is plentifully supplied with 

 blood-vessels, whose arterioles are surrounded by denser lymphoid 

 tissue that here and there swells out to form nodules often spoken of 

 as Malpighian corpuscles. 



The Tonsils. These are also composed of masses of lymphoid 

 tissue covered over by a stratified mucous membrane, the surface of 

 which is pitted with tiny pores leading into tube-like recesses known 

 as the crypts of the tonsil. 



The Thymus. This organ is a fairly large, soft pinkish mass 

 lying in the anterior end of the thoracic cavity around the bases of 



