THE VISCERA. 235 



antic., adipose and uniting tissue which is connected above with that 

 on the anterior part of the neck, below with that of the anterior ab- 

 dominal parietes. 



2. Cavum mediastini postici, more spacious than the anterior, not oblique, 

 bounded before by the pericardium and roots of the lungs, behind by 

 the bodies of the dorsal vertebra, laterally by the posterior mediastini ; 

 contains : 



aorta thoracica, (Esophagus, nn. vagi, duct, thoradcus, w. azygos and hemi- 

 azygos, uniting tissue, gland, mediast. post. 



d. Pleura pulmonalis is formed by the mediastini of the roots 

 of the lungs, the vessels passing in and out of which they en- 

 velope, being reflected upon the internal surface of each lung, 

 and firmly attached covering the external surface ; also entering 

 between the lobes, and forming ligg. interlobularia. Thus also 

 there remains between JPleura pulmonalis and the other portions 

 of the Pleura a closed cavity, the smooth moist walls of which 

 frequently secrete a serous fluid, lie close together, and (frequently) 

 are in places united with each other. 



Vessels are doubtful. Branches of the neighbouring intercostales, mammarue 

 internee, phrenicce siiperr., &c., form a capillary network which manifests itself 

 in inflammation, but only on the external surface of the Pleura. Lymphatics : 

 numerous, open into pkx. mammar. and inter cost alis. Nerves : not yet 

 found out. 



469. Thymus Gland, Glandula thymus, 



the sweetbread, a so-called blood gland, grows from the third 

 month of foetal life until the termination of the first year after 

 birth, then by degrees diminishes from below upwards, and en- 

 tirely disappears with the twelfth year. In its complete perfec- 

 tion it consists of two lateral lobes (only associated by uniting 

 tissue) so that properly we must admit two flat, three-cornered 

 thymus glands above and below pointed, which are situated in 

 the superior part of cavum mediastini antici, before the junction 

 of the vv. anonymae, behind the manubrium sterni, reach as far 

 upwards as the thyroid gland, and contain a large cavity filled 

 with white fluid (F. W. Becker), with which the cavities of the 

 lobules, the size of a pea, are connected. The cavity is not 

 bounded by a proper membrane. Astley Cooper maintained that 

 a large lymphatic vessel, which opens into the vena anonyma, 

 served as an excretory duct. 



The Parenchyma is, like that of the thyroid gland, pale red. The lateral 

 lobes divide into three or four larger, and these again into a number of 

 smaller lobuli, which are associated together by uniting tissue, in which fat 

 cells are present. The corpuscles which exist in the lobules, resemble the 

 nuclei of the blood discs and the globules of demolished nerve substance 

 (Ehrenberg). 



Vessels: Artt. thymica come from art. mammaria interna and subdavia, 



