540 RESPIRATORY SYSTEM OF THE OX 



THE TRACHEA 



The trachea is shorter than that of the horse, the average length being about 

 26 inches (ca. 65 cm.). Its caliber is relatively small, the width being about an 

 inch and a half (ca. 4 cm.) and the height about two inches (ca. 5 cm.)r The rings 

 are smaller, and number about fifty. At the beginning of the tube their free ends 

 are separated by a varying interval,' so that the tube is flattened and membranous 

 dorsally; but further back the ends are in apposition, so that they form a ridge 

 dorsally. The trachea is adherent to the right lung from the second rib backward. 

 The bifurcation is opposite the fifth rib, about the junction of its middle and ventral 

 thirds. 



In the sheep the average length of the trachea is about nine or ten inches (ca. 

 25 cm.) and its caliber a little less than an inch (ca. 2 cm.). 



THE BRONCHI 



There are three chief bronchi. The bronchus for the apical lobe of the right 

 lung (Bronchus apicalis) is detached from the trachea opposite to the third rib, 

 {. e., at a considerable distance anterior to the bifurcation. 



THE THORACIC CAVITY AND PLEUR.E 



The thoracic cavity is relatively small; it is especially short dorsally, and is 

 diminished laterally by the mode of attachment of the diaphragm to the ribs (vide 

 Myology). The endothoracic fascia is better developed than in the horse, and is 

 distinctly elastic. The pleura is also thick, and there are no perforations of the 

 mediastinum. The pleural sacs are even more unequal in extent than in the horse, 

 and the ventral part of the mediastinum is further to the left; in front of the peri- 

 cardium it is for the most part in contact \\dth the left wall of the chest. 



The diaphragmatic line of pleural reflection differs considerably from that of the horse in 

 conformity with the difference in the costal attachment of the diaphi-agm. It begins over the 

 space between the seventh and eighth costal cartilages, crosses the ventral end of the eighth rib, 

 and extends in a very slight curve upward and backward, so that it crosses the twelfth rib a Httle 

 above its middle and reaches to the last rib a short distance from its vertebral end. 



The pleura forms a cul-de-sac alongside of the body of the last thoracic vertebra. The right 

 pleural sac extends forward on the deep face of the scalenus a short distance beyond the first rib. 



THE LUNGS 



The difference in size between the two lungs is greater than in the horse, the 

 right lung weighing about half as much again as the left one. The average weight 

 of the lungs is about 73^ pounds (ca. 3 to 4 kg.) ; they form about yy^ of the body 

 weight. They are divided into lobes by deep interlobar fissures (Incisurae inter- 

 lobares). The left lung is divided into three lobes, named from before backward 

 apical, cardiac, and diaphragmatic (Lobus apicalis, cardiacus, diaphragmaticus). 

 The right lung may be regarded as having either four or five lobes. The apical 

 lobe is much larger than that of the left lung, and occupies the space in front of 

 the pericarchum, pushing the mediastinum against the left wall; it is usually sub- 

 divided into anterior and posterior parts by a deep fissure. The other lobes are 

 the cardiac, diaphragmatic, and intermediate, the last resembling that of the horse. ^ 



^ It has been customary to. consider the cardiac lobe to consist of two parts, as shown in Fig. 

 479. But the apical bronchus divides into two branches, the posterior of which goes to that 

 division of the lung which has been regarded as belonging to the cardiac lobe ; furthermore, these 

 parts of the lung are sometimes fused. It therefore appears desirable to include both as apical 

 lobe. 



