250 THE PIGEON 



(b) An anterior mesenteric artery, supplying the main portion of the intestme. 



(c) A pair of small anterior renal arteries to the anterior lobes of the kidneys. 



(d) A pair of femoral arteries to the thighs. 



(e) A pair of sciatic arteries, which give off small renal arteries to the median 



and posterior lobes of the kidneys and then pass to the legs. 

 (/) A pair of internal iliac arteries to the pelvis. 

 (g) A posterior mesenteric artery to the rectum and the cloaca. 

 (h) A caudal artery to the tail region. 



Notice that the pulmonary artery (referred to on page 246) crosses the 

 aorta ventrally and then divides into two. 



Make a complete sketch of the vascular system. (See Fig. 87, p. 248.) 



The Renal System. 



The kidneys (metanephros) are a pair of three-lobed solid organs lodged in 

 hollows of the pelvis. A small ureter passes from the ventral face of each 

 kidney backwards to open into the cloaca. At the front ends of the kidneys 

 are the small yellow, adrenal or supra-renal bodies. 



The Reproductive System. 



.(i) The Male. 



The testes are a pair of oval white bodies attached by peritoneum to the 

 front lobes of the kidneys. Each gives off a narrow and twisted duct, the 

 vas deferens, which, before opening into the cloaca, widens out into a small 

 vesicula seminalis. 



(ii) The Female. 



Only the left ovary persists, and it is situated between the front lobes of the 

 kidneys. It is attached to the dorsal body-wall, and usually contains eggs at 

 various stages of development. The left oviduct is a large coiled tube which 

 dpens internally (ccelomic funnel) near the ovary. Posteriorly it opens into the 

 cloaca. The right ovary atrophies during development, and only a vestige of 

 the right oviduct remains. 



Make a complete sketch of the renal and reproductive systems. {See Fig. 

 87, A and B.) 



Third Day 



The Skeletal System (continued). 



Remove the skin and muscles from the head, neck, trunk and limbs so as to 

 expose as much as possible of the skeletal system ; or. alternatively, examine 

 a prepared skeleton of the Pigeon or the Fowl. 



Characteristic features of the Bird's skeleton are the lightness of the bones 

 (mostly marrowless and containing air cavities), the extensive fusion, and the 

 absence of epiphyses. 



A. The Appendicular Skeleton (the Girdles and Limbs). 



1. The Pectoral or Shoulder Girdle. 



(a) The clavicles, already noted in the first day's work, are fused together 

 at their lower ends to form the furcula or " merry-thought " bone. 



