384 COMPARATIVE SPLANCHNOLOGY. 



is the possession of two uteri, each uterus opening into the vagina by a 

 distinct orifice ; the two are near together posteriorly, and anteriorly they 

 diverge. The vulva has both major and minor labia, and the clitoris is large 

 and very prominent. 



" The following principal forms of uterus are found in the mammalia : — 

 The simfh uterus (uterus simplex), in woman and the monkey ; the two-horned 

 uterus (uterus bicornis), in the mare and ruminant ; the bifurcated uterus 

 (uterus divisus), in the sow and carnivora ; and the double uterus (uterus 

 duplex), in the rodent." — Franck. 



AVES. 



For many reasons, this part of the subject is interesting, but very little 

 space can be given here to its discussion. 



Birds have no teeth, the maxillee being covered anteriorly, on the outside, 

 by a horny modification of the integument, the whole constituting the 

 rostrum or beak. The tongue is horny in structure, and apparently an organ 

 of prehension, not of taste. The (esophagus is very long, and its longi- 

 tudinal muscular coat is internal, the circular external. In seed-eating 

 birds, the oesophagus expands in the cervical region into the ingluvies, or 

 crop — a large sac which rests upon the fascia connecting the clavicles, and in 

 which maceration of the food is carried on. The oesophagus is then con- 

 tinued and expanded into the first cavity of the stomach, the proventrictdus^ a 

 very vascular and glandular cavity, where a fluid analogous to the gastric 

 juice is secreted. To this portion succeeds the second or muscular cavity, 

 the gizzard, which is oval and flattened in shape, but with a structure vary- 

 ing according to the nature of the animal's food. In granivorous or seed- 

 eating birds, the muscular coat possesses extraordinary thickness and strength, 

 while the lining membrane exhibits a dense, horny, epithelial structure. 

 In the upper portion are two orifices, a large one opening into the proven- 

 triculus, and just to the right of this a smaller pyloric orifice opening into the 

 duodenum. All the domesticated birds possess a gizzard similar to this, but 

 in those birds which feed naturally on flesh, the walls of the gizzard are mem- 

 branous in their thinness, the development of the organ being usually 

 correlated with the size of the ingluvies. 



Granivorous birds always swallow a quantity of stones or sand, which is 

 deposited in the gizzard, and with the action of the muscular wall and horny 

 lining, assists in grinding the ingesta to a pulp. Thus the gizzard may be 

 viewed as an organ of mastication. 



The intestines are very much shorter than in the mammalia, the layers of 

 muscular fibre being inversely arranged, as in the oesophagus. There are two 

 separate cceca, long and narrow, with their blind ends directed forwards. The 

 duodenum forms a loop or bend near its origin, embracing the pancreas ; the 

 rest of the small intestine is suspended by a mesentery. The large i7itesti7ie is 

 very short, running straight from the coeca to the termination of the canal ; it 

 is commonly termed the rectum, and it. opens into a cavity called the cloaca, 

 an excretory recess, common to the alimentarij, urinary, and genital systems. 



The pancreas usually consists of two distinct pieces, and its ducts are two in 

 number, opening separately into the duodenal loop. The liver is very large, 

 and as the diaphragm is rudimentary, it can hardly be regarded as a pure 



