380 SMITHSONIAN MISCELLANEOUS COLLECTIONS [VOL. 50 



The Medial Chamber 



The medial chamber contains the trachea and its bifurcation ; it 

 reaches posteriorly to the heart, dorsally to the sacci cervicales and 

 the oesophagus and laterally to the two lateral chambers. Along its 

 lateral walls run the common carotid arteries and the jugular veins. 

 It pushes a diverticulum, the diverticulum subcordale (fig. 2, DSC) 

 backward between the heart and the sternum. This diverticulum 

 does not reach the posterior margin of this bone, but it extends a good 

 deal farther than the heart, so that the designation given it by Ulrich 

 (1904, p. 332), diverticulum praecardiale, must be replaced by diver- 

 ticulum subcordale. There is also a well-developed diverticulum 

 supracordale. This arises behind the former, and is therefore not 

 visible in the section represented in fig. 2. It is rather short, and, 

 unlike the former, somewhat compressed. In the deltoid opening 

 traversed by the arterias carotides communes, the medial chamber 

 bulges markedly forward, and thus forms the diverticulum cesoph- 

 ageo : tracheale (figs. 7 and 11, DOETR), which, according to Ulrich 

 (1904, p. 331), extends forward right to the head. This diverticu- 

 lum is not bilaterally symmetrical. It lies between the oesophagus 

 and the trachea, and partly surrounds the latter — not wholly, part 

 of the trachea being attached to certain muscles of the neck. 



The Lateral Chambers 



The two lateral chambers are symmetrical with each other. They 

 occupy the remainder of the space whose limits have been described 

 above, and give oft the diverticula costalia (figs. 2 and it, DC) pos- 

 teriorly (cf. Roche, 1891, p. 64). These diverticula occupy the 

 space between the heart and the sterno-costal bones, and together 

 with the diverticula of the medial chamber, described above, form a 

 pneumatic investment which surrounds the whole of the anterior, 

 larger portion of the heart. Besides these intrathoracic diverticula, 

 extrathoracic diverticula are also given off from the lateral cham- 

 bers. These are the diverticula subscapularia, suprahumeralia, and 

 sternalia. 



The Diverticulum Subscapulars 



From each lateral chamber of the interclavicular sac a wide 

 diverticulum, the diverticulum subscapulare (figs. 7, II, and 12, 

 DSSCi), arises. This follows the ligamentum sterno-furculare 

 upwards, and, bending backwards farther on, it passes between the 

 upper end of the coracoid and the vertebral column along the brachial 

 plexus. Here only this plexus and a thin membrane separate it from 



