SI4 BIRDS. 



gastrics or by the division of the caudal vein, a coccygeo- 

 mesenteric arises, which receives vessels from the cloaca and 

 large intestine, and is continued along the mesentery to join 

 the hepatic portal system. 



As there are rarely any valves in the renal portal veins, 

 the blood from the viscera and hind-limbs can pass freely 

 either through the iliac veins and thence to the inferior vena 

 cava, or through the coccygeo-mesenteric vein to the hepatic 

 portal system. 



The epigastric vein of the bird takes blood from the fat- 

 laden sheet or great omentum which covers the abdominal 

 viscera. It leads not into the liver, but into one of the 

 hepatic veins. 



Associated with the blood-vascular system, there is a 

 lymphatic system with a few lymphatic glands. The spleen 

 lies on the right side of the proventriculus, the paired 

 thyroid lies beside the origin of the carotid arteries, and a 

 paired thymus is found in young birds in the neck region. 



Respiratory System. — The important facts are, that there 

 is as yet no diaphragm, that some of the bronchial branches in 

 the lungs are continued into adjacent air-sacs, that expiration 

 is a more active process than inspiration. 



The nostrils lie at the base of the beak overlapped by 

 the cere. Only in the kiwi are they at the tip of the beak. 



The trachea is strengthened by bony rings, and is moored 

 to the sternum by two sterno-tracheal muscles. It has a 

 larynx at its anterior end, and a syrinx at its lower end 

 where the bronchi diverge. The bronchial tubes branch in 

 a sort of tree-like fashion in the lungs. These lie attached 

 to the dorsal wall of the thorax, indented by six of the ribs, 

 and are covered with pleural membrane on their ventral 

 surface only. 



Around the lungs, and connected with the ends of some 

 of the bronchial tubes, are nine air-sacs, four being lateral 

 and one median. In order from behind forwards, lie pos- 

 terior or abdominal sacs, the posterior thoracics, the anterior 

 thoracics, the cervicals, and the interclavicular in the middle 

 line in front. The anterior and posterior air-sacs are con- 

 tinuous with air-spaces in the bones. 



Excretory System. — The kidneys are three-lobed, and lie 

 embedded in the ilia. They receive blood from the dorsal 



