246 



Name the Principal Air -sacs of the Pigeon, and state where 

 situated. 



Two cervical air-sacs, at base of neck in front of the lungs. 

 One interclavicular, between the two clavicles and surround- 

 ing the lower end of the trachea ; it has several diverticula, 

 and is connected with the axillary air-sacs of the shoulder. 

 Two anterior thoracics, two posterior thoracics, and two 

 abdominals, situated along the sides of the body, beneath 

 the ribs. 



Describe the Heart and Principal Blood-vessels of the Pigeon, 

 and indicate the General Course of the Circulation. 



The three venae cavae, conveying the impure blood from 

 the body, open into the right auricle ; thence the btbod 

 passes through the right auriculo-ventricular aperture into 

 the right ventricle, which is round the right side of the left 

 ventricle. The right auriculo-ventricular valve, guarding the 

 opening, is muscular and is connected with the ventricle 

 wall. From the left side of the right ventricle anteriorly, 

 the pulmonary artery arises ; its opening is guarded by three 

 crescentlc semilunar valves, and it divides into two branches, 

 conveying the impure blood to the lungs. The pure blood 

 returns from the lungs by pulmonary veins, which open 

 into the dorsal wall of the left auricle, and passes through 

 the left auriculo-ventricular aperture into the left ventricle. 

 The left auriculo-ventricular or mitral valve is a double 

 membranous flap attached by chorda tendineae to papillary 

 muscles of the ventricle wall. The blood is pumped to 

 the body through the single aortic arch ; it arises from the 

 right side of the ventricle anteriorly, and its opening is 

 guarded by three semilunar valves. 



The right and left superior venae cavae, which ojsrry 

 impure blood from the sides of the head and neck, are each 

 formed by the union of jugular, brachial, and pectoral veins. 

 The caudal vein divides into two " renal portals " and a 

 coccygeo-mesenteric, which passes forward to join the 

 hepatic portal vein (formed by union of gastro-duodenal, 

 anterior and posterior mesenteric veins, and going to the 

 liver). Each " renal portal " receives an internal iliac from 

 the pelvic wall, and, passing into the kidney, is there joined 

 by the sciatic, the femoral * and renal ; and it leaves the 

 kidney as a common iliac. The two iliacs join to form tho 

 inferior vena cava, which passes through the right lobe of 

 the liver and receives the hepatic veins. The epigastric vein, 

 from the great omentum, joins one of the hepatics. Tho 

 aortic or systemic arch gives off right and left innominate 



