526 THORAX OF THE FCETUS. 



Between the bronchial and pulmonary arteries and veins, 

 there is an intimate anastomosis so that either system of ves- 

 sels may be filled by forcing a fine injecting fluid through the 

 other. The cells of each lobule, according to Professor Homer, 

 Cloquet, and some other anatomists of distinction, communi- 

 cate laterally with each other. Reisseissen, Gerber, and other 

 microscopists, figure each on as a perfect cul de sac ; the 

 development of the lungs in the foetus resembling in its early 

 stages very closely that of the compound glands. The diame- 

 ter of these cells has been measured by Weber of Leipzig,* 

 by the aid of a micrometer attached with extreme care and 

 ingenuity to a microscope. According to him they are upon an 

 average about ^ part of an inch in diameter, which makes them 

 five or* six times larger than the cells of the parotid gland, and 

 fifteen or twenty times larger than the finest capillary blood- 

 vessels measured on a portion of skin which had been very 

 perfectly injected by Dr. Pockels of Brunswick. 



The Thorax of the Fcetus. 



In the cavity between the lamina of the mediastinum, where 

 they approach each other from the first ribs, is situated, a sub- 

 stance which is denominated the 



Thymus Gland. 



This substance gradually diminishes after birth, so that 

 in the adult it is often not to be found ; and when it exists it is 

 changed in its texture, being much firmer, as well as greatly 

 diminished. 



In the foetus it is of a pale red color; and during infancy 

 it has a yellowish tinge. It generally extends from the thyroid 

 gland, or a little below it, to the pericardium. From its supe- 

 rior portion two lateral processes are extended upwards : below, 

 it is formed into two lobes, which lie on the pericardium. 



If an incision be made into its substance, a fluid can be 



* Meckel's Archiv. fur Anat. and Physiol., 1830. 



