THE ALIMENTARY APPARATUS. 243 



Splenic artery, remarkable for its size and tortuosity, divides 

 in the hilus into four or five branches, each distributed to a 

 segment, terminating in a capillary plexus without anastomoses, 

 or. opening directly into the areolse of the splenic pulp. 



Splenic vein commences in the same manner as the arterioles 

 end, and empties into the portal vein. The smaller veins anas- 

 tomose freely. 



Nerves are from the splenic plexus, formed from the right 

 pneumogastric nerve, and the left semihmar ganglion of the 

 solar plexus. 



THYROID GLAND. The thyroid is a vascular, glandlike body, 

 situated on the sides of the upper part of the trachea, and con- 

 sists of two lateral lobes connected by a transverse portion, the 

 isthmus. 



A third lobe the pyramid sometimes arises from the left 

 lobe or upper margin of the isthmus. 



Levator glandular thyroidece are muscular bands sometimes 

 found passing from the isthmus to the body of the hyoid bone. 



Structure. This is similar to other glands, being made up 

 of a capsule and radiating septa inclosing alveoli the closed 

 rr sides each of which is lined with one layer of columnar 

 epithelium, and contains more or less viscid, transparent fluid 

 the colloid substance. The closed vesicles are abundantly sup- 

 plied with blood by meshes of capillaries, while penetrating the 

 septa are lymphatic net-works, and lymph sinuses are found in 

 the tissue between the vesicles and septa. 



Arteries are the superior thyroid, a branch of external 

 carotid, and inferior thyroid, a branch of the thyroid axis, and 

 sometimes a branch from the arch of the aorta or innominate 

 artery, the middle thyroid, or arteria thyroidea ima. All the 

 vessels anastomose freely. 



Veins form plexus about the gland and give off the superior 

 and middle thyroid to internal jugular, and inferior thyroid to 

 innominate vein. 



Nerves, from middle and inferior cervical ganglia and from 

 pneumogastric. 



THYMUS GLAND. The thymus gland is a temporary organ 

 of unknown function which attains its full size at the end of two 

 years and at puberty has almost disappeared. It occupies the 

 upper part of the anterior mediastinum, and is in relation in 

 front with the sternum, and below with the pericardium, aorta, 

 left innominate, and trachea. It is a flat, triangular body, com- 

 posed of a pair of lateral unequal lobes, about two inches in 

 length, one and one-half inches at the widest part, and one- 

 quarter inch thick, and weighing about one-half ounce. 



