154 ELEMENTS OF MAMMALIAN ANATOMY. 



of the thoracic duct is expanded, forming the receptaculum 

 chyli. Numerous valves are present in the duct, and give 

 to it a moniliform or beaded appearance. It receives all the 

 lymph from the left abdominal wall, both pelvic extremities, 

 a large part of the thoracic wall, and the thoracic and ab- 

 dominal viscera. 



DUCTLESS GLANDS. 



The spleen, thyroid gland, thymus gland, and suprarenal 

 bodies are ductless glands whose functions are imperfectly 

 known. The largest of these is the spleen, which is of a 

 deep red color in a fresh specimen, and lies in the abdominal 

 cavity on the left side caudad to the stomach (Fig. 55). 

 It is about five centimeters long, two centimeters wide, and 

 less than a centimeter thick. It is composed of lymphoid 

 tissue of two forms, supported by connective-tissue tra- 

 beculae which are merely prolongations of the enveloping 

 capsule. The two forms of tissue can be seen by cutting 

 the organ transversely. The dense lymphoid tissue appears 

 as white spots less than the size of a pin-head. They are 

 the Malpighian corpuscles. The intervening looser lymph- 

 oid tissue forms the greater part of the spleen, and is known 

 as the splenic pulp. The splenic artery, a branch of the 

 coeliac axis, enters the spleen at its hilus and divides into 

 capillaries which terminate in irregular spaces, thus per- 

 mitting the blood to flow freely through the splenic pulp, 

 whence it is taken up by the capillaries of the splenic vein 

 leading to the portal vein. In embryonic life the spleen 

 forms blood-corpuscles, but in postnatal life it seems to 

 destroy blood-corpuscles. An animal from which the 

 spleen has been removed may live many years in good 

 health. 



The thyroid gland is composed of two parts lying on 

 the lateral aspects of the trachea, just caudad to the larynx. 



