3 o6 VETERINARY LECTURES 



They are held together by ligaments, and moved by muscles. The 

 cavity of the larynx is lined by a very sensitive mucous membrane. 



479. Trachea (Plate XXX VI., No. 8), or windpipe, is a long 

 tube running from the larynx to the roots of the lungs, where it 

 divides into two bronchi. It is made up of a number of ring-shaped 

 pieces of cartilage, held together by elastic ligamentous tissue, and is 

 thus capable of flexible movement. It is lined internally with mucous 

 membrane. 



480. Thyroid Gland (Plate XXXVI., No. 20).— This gland is 

 ductless, and consists of two lobes placed one on each side of the 

 trachea, near its junction with the larynx. It is larger in the young 

 than in the aduit animal. 



481. Thymus Gland (Plate XXXV L, No. 19) is a single body, 

 found lying on the under side of the trachea at the entrance to the 

 chest. It is large in the very young animal, but gradually disappears 

 after birth. The functions of the thyroid and thymus glands are not, 

 as yet, perfectly understood. Although described in this place, they 

 have nothing to do with respiration. 



482. Bronchi (Plate XXXVI., Nos. 10 and 11) are two in 

 number, one going to the right lung and the other to the left. They 

 divide and subdivide, ramifying through the substance of the lungs, 

 until they are too small to be seen by the naked eye. The smaller 

 branches and the air cells in which they terminate form clusters 

 called lobules. The divisions and subdivisions resemble a tree with 

 branches, the air cells resembling the leaves. 



483. Lungs, or Lights (Plate XXXVI., Nos. 12 and 13)— right 

 and left — are the principal organs of respiration. They are of a fine, 

 soft, spongy texture, pale pink in colour, and very light and porous, 

 owing to the air cells containing air ; as a consequence, the lungs can 

 float in water. In the horse the right lung is divided into three lobes, 

 and the left lung into two, while in the cow the right is divided into 

 four lobes and the left into two. The interlobular tissue is also 

 found in greater abundance in the cow than in the horse, The nutrient 



