ELEMENTAR Y ANA TOMY. 



[LESS. 



This organ may be relatively much larger than in man, 

 and consist of two lobes, as in the Ornithorhynchus ; it 

 may consist of three lobes, as in the Echidna. Occasionally in 

 Rodents a small detached accessory spleen may be developed, 

 and there are constantly accessory spleens in the Sturgeon, 

 the Dolphin, and Nanvha'. 



v.c.r. 



Ao. 



Z>m. 



FIG. 408. -THE SPLEEN (S//.) with the splenic artery (SpA\ Below this latter 

 is seen the splenic vein running to help to form the vena portce (VP). 



Ao, the aorta ; Z>, a pillar of the diaphragm : PD, the pancreatic duct exposed by 

 dissection in the substance of the pancreas ; Dm, duodenum ; BD, the biliary 

 duct opening into the pancreatic duct at x ; y, the intestinal vessels. 



13. The THYROID GLAND of man is a soft, reddish, and, 

 very vascular body, embracing the trachea in front, and 

 ascending to the larynx. It has no duct, and is of a more 

 or less semilunar form, with two lateral lobes, united by an 

 isthmus. It is covered by the sterno-hyoid, sterno-thyroid, 

 and omo-hyoid muscles. 



In that man develops a thyroid gland he appears to agree 

 with all Vertebrates except the Lancelet. 



This body may consist of two completely divided lateral 

 halves,, placed each on one side of the trachea and larynx, as 

 in Birds, Batrachians, Monitors, the Llama, the Otter, the 

 Mole, and others, and as even in the Orang. It may consist 

 of one undivided body, as in Cetaceans. 



It may be represented (as in Birds) by small rounded or 

 elongated bodies, very vascular, placed beside the trachea, 

 above the syrinx, and closely connected with the carotid or 



