76 EVERs's COMPARATIVE ANATOMY. 



tion of the cloaca are the openings of the ureters, and external to 

 these, the openings of the oviducts, or vasa deferentia. 



To this urethro-sexual canal, succeeds the preputial cavity, or 

 lower portion of the cloaca, which lodges the organs of excitement, 

 clitoris or penis, as in reptiles, marsupial, and monotrematous mam- 

 malia. In the median plain, and on the dorsal aspect of the prepu- 

 tial cavity is the opening of a conical sac, named Barsa Fibricii, 

 which lodge's the anal follicles, and is analogous to Cowper's glands. 



The liver is large in birds, especially in the aquatic species, it 

 generally consists of two lobes, but occasionally of three, as in the 

 pigeon, goose, and swan ; the right lobe is usually larger than the 

 left, the latter, however, is larger in the bustard, where it extends 

 into the pelvis. The bile is discharged by two ducts, one goes 

 directly to the duodenum, the other to the gall-bladder, and when 

 the latter is absent, they both open separately into the duodenum, 

 but in no case is there a ductus choledochus. The pancreas, long, 

 narrow, and trihedral, is lodged in the fold of the duodenum, its 

 ducts are two, sometimes three in number, as in the pigeon, raven, 

 and common fowl, and they terminate separately in the duodenum. 

 The small, round, oval, flat, or elongated spleen is placed beneath 

 the liver, and to the right of the proventriculus; its texture is loose, 

 and the blood would seem to be deposited in cells, from which the 

 veins take it up. 



When we contemplate the different lengths and forms of intestine 

 met with in this class, we cannot help attributing it to some wise 

 purpose, and a little reflection on the greatly diversified nature of 

 the food on which the various tribes of birds are destined to subsist, 

 irresistibly leads us to infer that economy seems to be the main 

 design ; for instance, the colon and coeca of the African ostrich, 

 which has to subsist on the scanty and uncertain fare of the desert, 

 are fifty times the length of the same parts in the cassowary, which 

 inhabits Java, one of the most fertile countries on the globe. 



MAMMALIA. 



The digestive organs vary more in this than in any other of the 

 vertebrated classes, and the varieties will be found to refer chiefly 

 to the type of development and living habits of the sundry species. 

 The teeth present infinite varieties as to form and position ; however, 

 their density and fixedness are well calculated to disintegrate ali- 

 mentary substances, and blend them with the mucous and salivary 

 secretions. The teeth are wanting in the ant-eaters, pangolins, and 

 the whalebone whale. The young ornithorhynchus paradoxus has 

 two molar teeth in each jaw on each side: these are shed in the 

 adult animal, and replaced by one large one on each side. But in 

 the hystrix there are twenty small, blunt, horny teeth, near the base 

 of the tongue, and seven transverse rows in the corresponding sur- 

 face of the palate. The incisor, canine, and molar teeth exist in 

 the quadrumana. carnivora, ruminantia, without horns, and in most 



