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- 
beculee 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 
cceliac 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. 
