90 3fam77ialia, 



DUCTLESS, OE YASCULAE GLAXDS. 



i. The Spleen-. 



The Spleen is always present, lies near the Stomach, and 

 is commonly elongate and simple; but varies in form and 

 size in the several Orders. Its development is directly cor- 

 related with that of the Pancreas. It is larger in the om- 

 nivorous and quasi-carnivorous Eodents, e.g. the Eats, than 

 in the vegetarian species of the Order ; it is also relatively 

 larger in the Sectorialia than in the Ungulata. 



Cete. In some Cete, e.g. Dolphin, the Spleen is remarkable for 

 its sub-divisions. 



Marsupialia. In most Marsupials the Spleen is bent, or bilobed. 



2. The Thyroid.* 



A Thyroid gland is generally present, situated in close 

 relation to the Larynx, from the shield-shaped cartilage of 

 which it has received its name. It usually consists of a pair 

 of oblong lateral lobes, united by ligament. 



3._The Thymus. 



This gland, which is formed towards the end of foetal 

 existance, and attains its greatest development during the 

 period of lactation, is present in most Mammals at birth ; the 

 bulk of the gland lies behind the manubrium. It is distin- 

 guished from the Thyroid by its wide central cavity, and 

 generally by its diminution in volume, or disappearance, 

 early in life. 



* QvptoQj a shield ; iihoQy shape. 



