THYMUS GLAND. 



1089 



portion of the thymus, the platysma myoides 

 and external jugular vein are first turned 

 aside, and the origins of the sterno-mastoidei 

 muscles are raised; when this has been accom- 

 plished, the sterno-hyoidei appear covering 

 and passing over the thymus gland. The 

 sterno-thyroidei muscles . . . cover this organ 

 anteriorly; but when they are removed, the 

 cervical portions of the thymus are seen on 

 the anterior and lateral parts of the trachea, 

 and just below the thyroid gland, where it 

 passes on the fascia on the fore part of the 

 air tube, and unites with the larynx by liga- 

 ment." 



" The internal jugular veins are placed an- 

 teriorly and laterally to the cervical portion, 

 and the carotid arteries, with the par vagum, 

 appear more externally." 



" The first bone of the sternum and sternal 

 ends of the clavicle cover the junction of the 

 cervical with the thoracic portion of this 

 gland." 



" In many of the subjects which I have ex- 

 amined, the cervical portion of the thymus 

 passes higher upon the right than on the left 

 side, and I have generally seen it joined by a 

 ligament to the larynx, and by vessels to the 

 thyroid gland." 



In a human foetus, at about the fourth-and- 

 a-half month, I found the thymus consisting 

 of two lateral portions, of which the right was 

 the larger (in another of similar age the left 

 was) ; this portion extended downward, lying 

 upon the pericardium, as far as opposite the 



right auricular appendix, and reached upwards 

 only to the left brachio- cephalic vein, which it 

 did not cross ; the left extended downwards, 

 over the pericardium, to a point opposite the 

 middle of the trunk of the pulmonary artery, 

 and passed up, lying upon the vena transversa, 

 and afterwards upon the side of the trachea, be- 

 tween it and the common carotid, till it arrived 

 at the level of the bifurcation of the arteria 

 innominata. 



The appearance of the gland in the fetus 

 about the middle of utero-gestation is precisely 

 similar to that of the salivary gland in the 

 same ; it is beautifully tabulated, and sur- 

 rounded by an atmosphere of nascent areolar 

 tissue. In the more perfectly formed con- 

 dition it is surrounded by an envelope of 

 coarse cellular membrane, which penetrates 

 the intervals of its larger divisions, unites the 

 right and left portions together, and forms a 

 general envelope, by which it is connected to 

 the surrounding parts. 



In examining the structure of the thymus, 

 we are conducted by two eminent guides to 

 conclusions almost identical, though by dif- 

 ferent modes of proceeding. This coincidence 

 is of great value, and we can scarcely enter- 

 tain a moment's doubt of its being founded on 

 real truth ; it may therefore be well to notice 

 separately the modes of investigation above 

 referred to. 



Sir A. Cooper, by skilful manipulation, suc- 

 ceeded in unravelling the gland, and showed 

 each lateral part to be composed of a 



Fig. 721. 



Tf,e rif/ht and left tliymus gland injected with wax and partially unravelled. In one are seen the rope, tlie 

 lobes, and the cells, m the other the communication between the thoracic and cervical portions. 

 .Sir A. Cooper.) 



