558 FCETAL LUNGS AND HEART. 



The Arteries of the thymus gland are derived from the internal 

 mammary, and from the superior and inferior thyroid. 



The Veins terminate in the left vena innominata, and some small 

 branches in the thyroid veins. 



The Nerves are very minute, and are derived chiefly through the 

 internal mammary plexus, from the superior thoracic ganglion of 

 the sympathetic. Sir Astley Cooper has also seen a branch from 

 the junction of the pneumogastric and sympathetic pass to the side 

 of the gland. 



The Lymphatics terminate in the general union of the lymphatic 

 vessels at the junction of the internal jugular and subclavian veins. 

 Sir Astley Cooper has injected them only once in the human foetus, 

 but in the calf he finds two large lymphatic ducts, which commence 

 in the upper extremities of the glands, and pass downwards, to ter- 

 minate at the junction of the jugular and subclavian vein at each 

 side. These vessels he considers the " absorbent ducts of the glands ; 

 * thymic ducts ;' they are the carriers of the fluid from the thymus 

 into the veins." 



Sir Astley Cooper concludes his anatomical description of this 

 gland with the following interesting physiological observations : 



"As the thymus secretes all the parts of the blood, viz. albumen, 

 fibrine, and particles, is it not probable that the gland is designed to 

 prepare a fluid well fitted for the foetal growth and nourishment 

 from the blood of the mother, before the birth of the foetus, and, 

 consequently, before chyle is formed from food ? and this process 

 continues for a short time after birth, the quantity of fluid secreted 

 from the thymus gradually declining as that of chylification becomes 

 perfectly established." 



FOETAL LUNGS. 



The Lungs previously to the act of inspiration, are dense and 

 solid in structure, and of a deep red colour ; their specific gravity 

 greater than water, in which they sink to the bottom, whereas lung 

 which has respired will float upon that fluid. The specific gravity 

 is, however, no test of the real weight of the lung ; the respired 

 lung being actually heavier than the foetal. Thus the weight of the 

 foetal lung, at about the middle period of uterine life, is to the weight 

 of the body as 1 to 60.* But, after respiration, the relative weight 

 of the lung to the entire body as 1 to 30. 



FCETAL HEART. 



The Heart of the foetus is large in proportion to the size of the 

 body ; it is also developed very early, representing at first a simple 

 vessel, and undergoing various degrees of complication until it ar- 

 rives at the compound character which it presents after birth. The 



* Cruvelhier. Anatomie Descriptive, vol. ii. p. C21. 





