THE LUNGS 551 
five U-shaped rings; the ends of the rings do not meet dorsally, so that here the 
trachea has a membranous wall (Paries membranacea), and is composed of a layer 
of transverse smooth muscle-fibers outside of the rings, the fibrous membrane, and 
the mucous membrane. 
The stem-bronchi diverge at an obtuse angle, and each divides into two 
branches before entering the lung, but the ramification differs in the two lungs. 
In the right lung the anterior bronchus goes to the apical lobe, and the stem- 
bronchus gives off a branch to the cardiac lobe and another to the intermediate lobe. 
In the left lung the anterior bronchus divides into two branches for the apical and 
ardiac lobes. The anterior branch of the left bronchus crosses under the pul+ 
monary artery. 
THE LUNGS 
The lungs differ in shape from those of the horse and ox in conformity with 
the shape of the thorax, which is relatively very wide in the dog; the lateral thoracice 
walls are strongly curved, and the costal surface of the lungs is correspondingly 
convex. 
The right lung is much (ca. 25 per cent.) larger than the left. It is divided 
Dorsal border 
Cardiac notch 
Fic. 491.—Rreut Lune or Doc; Meprat View. 
L. a., Apical lobe; ZL. c., cardiac lobe; L. d., diaphragmatic lobe; L. i., intermediate lobe; 1, stem-bronchus; 2, 2, 
bronchi of apical lobe; 3, 3’, divisions of pulmonary artery; 4-7, pulmonary veins; 8, groove for anterior vena cava; 
9, groove for vena azygos; 10, groove for esophagus; 11, groove for trunk of vertebral, cervical, and dorsal veins; 12, 
groove for internal thoracic vessels. 
into four lobes by deep fissures which extend to the root. The lobes are the apical, 
cardiac, diaphragmatic, and intermediate. The apical lobe extends considerably 
over the median plane in front of the pericardium. The intermediate lobe has the 
form of an irregular, three-sided pyramid, with its base against the diaphragm and 
its apex at the root; on its lateral face there is a deep groove which contains the 
posterior vena cava and right phrenic nerve, enclosed in a special pleural fold. The 
cardiac impression of the right lung is much deeper than that of the left. The 
; The costal attachment of the diaphragm is lower than in the other animals, thus further 
Increasing the capacity of the thorax (vide diaphragm). 
