HAP. vii.j THE CATS ORGANS OF CIRCULATION. 199 



begin to arise from the epithelial investment of the trabeculce, and 

 only acquire their coats, other than epithelial, as they leave the 

 gland. ^ Thus^ a lymphatic gland is, as it were, an expanded 

 sinus into which a number of lymphatics merge, and wherein it 

 appears a multiplication of lymph corpuscles takes place, probably 

 by spontaneous division the parts of the corpuscles thus spontane- 

 ously dividing growing up into whole corpuscles. 



Each gland is richly supplied with blood-vessels, and the lymph 



CL.l. 



Fig. 101. DIAGRAMMATIC SKCTION OF A LYMPHATIC GLAND. 



aZ. Afferent lymphatics. 



el. Efferent lymphatics. 



c. Cortical substance. 



m. Medullary substance. 



Zs. Lymph sinus. 



c. Fibrous coat. 



tr. Trabeculse. 



Hi. Lymph corpuscles. 



The letter C is placed in one of the alveoli. The 

 trabeculse are represented by a dark shade, 

 and are seen extending inwards from the 

 fibrous coat and as spots in the medullary 



substance such spots being trabeculae cut 

 across. At the upper right-hand part of the 

 figure the lymph corpuscles, Hi, are repre- 

 sented in three alveoli and in the adjacent 

 medullary part. Elsewhere they are not 

 represented. A white band is to be seen 

 around all the alveoli, and also round each 

 of the cut-across trabeculse in medullary 

 substance. The band is the lymph sinus, 

 and the irregular lines which cross it at 

 short intervals are the connective tissue 

 fibres and nuclei. 



which leaves it is not only richer in colourless corpuscles than is 

 that which comes to it, but also in fibrin. These glands are 

 conspicuous in the neck, the axilla, and the thigh, and speedily 

 enlarge in size when any part of the body near them becomes the 

 seat of pain. 



8. The HEART is a thick muscular and hollow organ, from the 

 anterior, broad part of which great blood-vessels originate. 



It is enclosed in a sac of fibrous tissue lined with epithelium, 

 called the pericardium. It consists of four chambers, two of which 



