16 DISEASES OF DOMESTICATED BIRDS 
chial branch which leaves the respective lung on its posterior in- 
ferior surface. These sacs extend from the lungs to the cloaca and 
are the largest in the body. They supply the bones of the pelvic 
region and femur in those species in which these bones are aeri- 
ferous. The femur of the pigeon and the humerus of the ostrich 
have no air spaces but retain their marrow. 
URINARY SYSTEM 
The urinary tract is composed of two kidneys each drained by a 
ureter lying along its ventral face and proceeding caudad to empty 
into the cloaca posterior to the terminus of the rectum. The kid- 
neys are elongated, reddish brown bodies divided into three prin- 
cipal lobes. They are closely applied to cavities in the pelvis on 
each side of the spinal column. ‘These organs are not divided into 
macroscopically visible cortical and medullary zones as in mammals 
but have a homogeneous structure. In texture they are quite soft 
and rupture easily when pressed by the finger. The ureter does 
not originate in a renal pelvis but is formed by the union of several 
uriniferous tubules along the ventral face of the kidney. Its course 
may be traced by the white color of the urates which it carries, a 
material corresponding to the urine of mammals. 
GENERATIVE SYSTEM 
The male generative organs consist of two testicles each provided 
with a vas deferens or excretory duct. The testicles are oval shaped 
organs situated in the sub-lumbar region at the anterior extremities 
of the kidneys. They vary greatly in size at different seasons, but 
show a remarkable development during the breeding season. The 
two vasa deferentiz pass along the kidneys by the side of the 
ureters, exhibiting transverse convolutions along their course. 
Each opens on a small papilla situated in the uro-genital division 
of the cloaca. The base of each papilla is surrounded by a plexus 
of blood vessels which serve the purpose of an erectile tissue during 
coitus. In the drake and gander a long single penis is developed. 
The female generative organs consist of a single ovary and an 
oviduct situated on the left side of the abdominal cavity. The 
right ovary and oviduct usually fail to develop. Occasionally a rudi- 
mentary right oviduct is present. In one actively laying hen Gal- 
lagher observed a right oviduct which was nearly as long as the 
