ANATOMY OF BIRDS 7 
by their frequent anastomoses. This is also true of the veins of 
birds. 
Veins. The blood is returned to the heart by three trunks, the 
two anterior vene cave and the posterior vena cava. The right 
jugular exceeds the left in size. The two communicate with each 
other by means of a cross branch at the base of the cranium. 
Lymphatics. The lymphatics of birds do not form two strata, 
a superficial and a deep seated, as in mammals. The latter only is 
observed. Lymphatic glands are few. The most conspicuous are 
located at the base of the neck and in the anterior thoracic cavity. 
They are replaced by plexuses of lymphatic vessels surrounding the 
principal blood vessels. From the aortic plexus arise two thoracic 
ducts which pass cephalad on the ventral surface of the lungs and 
terminate respectively in the jugular vein of the same side. 
NORMAL AVIAN BLOOD 
In birds as in mammals the blood is composed of a straw colored 
fluid or plasma in which float several types of blood corpuscles. One 
important difference between avian and mammalian blood, excepting 
the camel, is the presence of nuclei in the red corpuscles of the 
former. The formed elements or corpuscles are divided into two 
main divisions, the red cells or erythrocytes and the white cells 
or leucocytes. These elements vary greatly in number in different 
birds, and even in the same bird at different ages. Each cubic 
millimeter of an adult fowl’s blood contains approximately 3,250,000 
red cells and 26,000 white cells, giving a percentage relation of 125 
to 1. In certain pathologic conditions this relation is markedly 
changed, the red cells rapidly decreasing and the white cells increas- 
Ing in numbers. 
Red blood corpuscles or erythrocytes are straw colored, nucle- 
ated, oval, flattened discs, about 12 microns in length and 7.3 mi- 
crons in width. The nuclei take a deep blue stain with methylene 
blue, or Giemsa. The surrounding protoplasm takes a light yellow 
with methylene blue and a pink color with Giemsa’s stain. 
White blood corpuscles or leucocytes are nucleated, colorless 
cells, rounded or irregular in form. They exhibit ameboid 
movement in the blood stream, some being more actively motile than 
others. The variations in their size, character of the nuclei, pres- 
ence of granules and character of the inclosed granules differentiate 
these cells into five varieties. These varieties with their percentage 
ratio are as follows: 
