1350 



THE DUCTLESS GLANDS. 



Parathyreoid III. is normally drawn by the thymus, as it migrates, caudal to parathyreoid IV. 

 As a rule it halts at the level of the inferior extremijty of the lateral lobe of the thyreoid gland, 

 but may continue its descent into the thorax or may not descend at all. In the latter case it 

 remains near the bifurcation of the common carotid artery, where it is apt to be confused with 

 the glandula carotica. It is from this confusion th'at the idea, that the chromaphil glandula 

 carotica arises from the third pharyngeal pouch, has obtained a foothold in anatomical teaching. 



(iii.) THYMUS. 



Strictly, there are two thymus glands, a right and a left, but they are so 

 closely bound to one another that it is customary to speak of them as a unit, 



Sterno-hyoid muscle 

 - Sterno-thyreoid muscle 

 Sterno-mastoid muscle 

 Thyreoid gland 

 Internal jugular vein 

 Phrenic nerve 



Scalenus anterior 

 -Subclavian artery (left) 

 Left vagus nerve 

 Subclavian vein (left) 



Recurrent ner 

 Inferior thyreoid vein 



Right vagus nerve 



Bifurcation of inno- 

 minate artery 



Right subclavian 



Internal mammary 

 artery 



Right inno- 

 minate vein 



RIGHT LOBE OK 

 THYMUS 



Superior lob< 

 of right lun 



Common carotid artery 

 Left innominate vein 



First rib 

 Aortic arch 

 LEFT LOBE OF 



THYMUS 



Left lung 



Heart 



Pulmonary fisaur 



PTTL- Pericardium 



FIG. 1060. DISSECTION TO SHOW THE THYMDS GLAND IN AN ADULT FEMALE. 



the thymus. This is an irregular pinkish mass of glandular tissue placed in tl 

 lower part of the neck and in the superior and anterior mediastina. Its si: 

 varies, relatively and absolutely, with age, sex, and nutrition, being relatively 

 largest in infancy, absolutely largest at puberty; larger in females and the \\el 

 nourished than in males and the emaciated ; large in healthy adults accidentally 

 killed ; small in persons, even children, who have died of a slow wasting disease, 

 It is supposed that it undergoes a premature permanent involution as the resr u 

 of severe illness even though, to all appearance, the individual completely recove 



