544 RESPIRATORY SYSTEM OF THE OX 



On the left side the cardiac notch leaves the greater part of the pericardium in contact with the 

 chest wall as far back as the fourth intercostal space. On the right side the lung commonly covers 

 the pericardium, so that the latter has no contact with the lateral wall of the thorax. But in some 

 cases (as in the annexed figures) there is a small cardiac notch at the ventral part of the third rib 

 and intercostal space. In dissectmg-room subjects the basal border usually begins at the space be- 

 tween the fifth and sixth costal cartilages, crosses the ventral part of the sixth rib, and is then 

 about parallel with the diaphragmatic line of pleural reflection. It crosses the ninth rib about 

 its middle and ends at the vertebral end of the eleventh intercostal space. 



The lobulation is very distinct on account of the extremely large amount of 

 interlobular tissue. 



In the sheep the lungs resemble those of the ox in lobation, but differ from 

 them considerably in shape. They are relatively somewhat longer, and the basal 

 border differs in conformity ^^ath the diaphragmatic line of pleural reflection. 

 There is usually a small triangular cardiac notch on the right lung opposite to the 

 central part of the fourth and fifth ribs; its greatest height is about two inches 

 (ca. 5 cm.). The left lung leaves the greater part of the pericardium uncovered as 

 far back as the fifth intercostal space. The lobulation of the lung is much less 

 distinct than in the ox. The pleural sacs form a cul-de-sac on each side of the first 

 lumbar vertebra. 



In the sheep the diaphragmatic line of pleural reflection differs from that of the ox. It ex- 

 tends along the seventh and eighth costal cartilages, crosses the ninth cartilage close to the rib, 

 the ventral ends of the tenth and eleventh ribs, the twelfth rib about an inch (ca. 2-3 cm.) from 

 it.s ventral end, and the thirteenth rib about two inches (ca. 5 cm.) from its ventral end. It 

 reaches as far back as the anterior border of the first lumbar transverse process. 



THE THYROID GLAND 



The thyroid gland is softer in texture than in the horse and is pale in color in 

 the adult; in the calf it is dark red in color. The lateral loljes are irregularly 

 triangular in outline and are more extensive and flatter than in the horse. In 

 addition to their contact with the trachea they are related deeply to the oesophagus 

 and the crico-pharyngeus muscle to a varying extent. The superficial face is 

 related to the sterno-thjTO-hj'oideus, sterno-cephalicus, the carotid artery, internal 

 jugular vein, and the vagus and sympathetic nerves. The isthmus is constantly 

 present and glandular; it is band-like and is commonly a quarter to half .an inch 

 (ca. 0.5-1 cm.) in width. 



The lateral lobes average about three inches or more (ca. S cm.) in length and about half an 

 ounce (ca. 14-1.5 gm.) in weight. They are so soft and loose in texture that their true shape is 

 seen only in specimens hardened in situ. In soft material they appear o\-al in outline. The 

 isthmus may be connected with the ventral margin or the posterior end of the lateral lolDes; it is 

 relatively large in the calf, ami is very evident on account of its dark color. 



In the sheep the thyroid gland is dark red in color. The lateral lobes have a 

 long eUiptical outhne and he on each side of the first six or seven rings of the trachea; 

 they are two inches or more (ca. 5-fi cm.) in length and half an inch or more (ca. 

 1.5 cm.) in height. They are connected by a fiat glandular isthmus a quarter of 

 an inch or more (ca. 6-8 mm.) in width; the isthmus is connected "vvith the lateral 

 lobe at or near the posterior end of the latter, and crosses the trachea about the fifth 

 ring. 



Accessory thyroids may be found, and parathyroids also occur near the pos- 

 terior extremity or on the deep surface of the lateral lobes of the thyroid. 



THE THYMUS GLAND 



The thjrmus is pale and distinctly lobulated. It is much larger in the calf 

 than in the foal, weighing at five or six weeks about 15 to 25 ounces (ca. 425 to 600 

 grams). At the period of its greatest development it occupies the greater part of 

 the anterior mediastinal space, reaching back to the pericardium, pulmonary artery, 

 and aortic arch. Its left face (covered by the mediastinal pleura) is in contact 



