754 COMPARATIVE ANATOMY 



communicates with the intestine through a valve-shaped opening con- 

 trolled by a sphincter muscle. The cardiac end of the stomach may end 

 as a blind pouch. The organ is often sufficiently distensile to permit one 

 animal to swallow another as large as itself. The intestine is short but 

 of large diameter and has a secreting surface greatly enlarged by a fold 

 in the shape of a spiral staircase (present, however, in very few teleostei) 

 called the spiral valve. All primitive fish have this spiral valve. A large 

 bi-lobed liver, which is provided with a gall bladder and a bile duct, 

 opens into the intestine. The pancreas also pours its secretion into the 

 intestine. 



TURTLES 



The digestive system of reptiles varies somewhat in carnivorous 

 and herbivorous forms, but in all turtles it is comparatively simple In the 

 turtle there are no teeth. The tongue is broad and soft and cannot be 

 protruded. The stomach is a simple U-shaped enlargement of the ali- 

 mentary tract. The intestine is without a caecum ; it is clearly divided 

 into large and small intestines. The cloaca is proportionately large: 



AVES 



The mouth is hard aad narrow and the tongue is hard and often of 

 great functional value. The oesophagus which has many large cornified 

 papillae, develops an enlargement called the crop. The stomach has 

 a proventriculus which secretes the gastric juice, and a muscular gizzard 

 or gastric mill. The intestine is U-shaped, and is composed of duo- 

 denum, ileiim, and rectum. Between the ileum and rectum there are 

 two caeca. The rectum opens into a cloaca. There are two bile ducts 

 but no gall bladder. The pancreas empties into the duodenum. The 

 intestine is found to be longer and more coiled in ascending vertebrates. 

 In cyclostomes, teleostomes, and all non-placental mammals, the intes- 

 tine terminates in a cloaca, as do also the urinary and genital ducts. 

 In placental mammals and in cyclostomes and teleostomes the urinary 

 and genital ducts have a distinct and separate opening from that of the 

 intestine. 



MAMMALS 



In all vertebrates (except birds and mammals) the coelom consists 

 of the following two compartments : 



artery ; c v., caudal vein ; d, bursa Entiana ; f.L, falciform ligament appearing 

 on surface of left lobe of liver in which it is embedded ; i., intestine ; i.a., intestinal 

 branch of anterior mesenteric artery ; 1., lienogastric artery ; not., notochord ; ov., 

 ovary ; p., portal vein lying beside hepatic artery ; ps., pancreas with duct opening 

 into intestine ; py., pyloric limb of stomach ; r., rectum, between hinder ends of 

 oviducts, with rectal gland (r.gl.) attached to its dorsal side; sh., right shell gland 

 on course of right oviduct ; sp., spleen ; sp.c., spinal cord ; ur.p., urinary papilla ; 

 v., branch of portal vein formed by junction of intestinal and splenic veins. 



Besides the above, note nostrils : oronasal grooves ; mouth ; pectoral and 

 pelvic fins ; pericardial and abdominal cavities ; heart, consisting of sinus venosus 

 (behind), ventricle, auricle (showing at sides of ventricle), and conus ; cloaca, and 

 transverse section of tail, showing at the sides the myomeres, above the anterior 

 dorsal fin, and in the middle the cartilage of the backbone enclosing spinal cord, 

 notochord, and blood vessels. (After Borradaile. ) 



