THE VASCULAR SYSTEM. 1133 



sels commence in an intercommunicating system of clefts or spaces which have no 

 complete endothelial lining in the connective tissue of the different (.rirsins. They 

 have been named the rootlets of the lymphatics, and are identical with the spaces 

 in which the connective-tissue corpuscles are contained. This then is properly 

 regarded as one method of their commencement, when the lymphatic vessels are 

 apparently continuous with spaces in the connective tissue, and Klein has described 

 and figured a direct communication between these spaces and the lymphatic vessel. 1 

 But the lymphatics have also other modes of origin, for the intestinal lacteals 

 commence by closed extremities, though some observers believe that the closed 

 extremity is continuous with a minute network contained in the substance of the 

 villus, through which the lacteal is connected with the endothelial cells covering it. 

 Again, it seems now to be conclusively proved that the serous membranes present 

 stomata or openings between the endothelial cells (Fig. 672) by which there is an 

 open communication with the lymphatic system, and through which the lyrnph is 

 thought to be pumped by the alternate dilatation and contraction of the serous 

 surface, due to the movements of respiration and circulation, 2 so that the serous 

 and synovial sacs may be regarded, in a certain sense, as large lymph-cavities or 

 sinuses. Von Recklinghausen was the first to observe the passage of milk and 

 other colored fluids through these stomata on the peritoneal surface of the 

 central tendon of the diaphragm. Again, in most glandular structures the 

 lymphatic capillaries have a lacunar origin. Here they begin in irregular clefts or 

 spaces in the tissue of the part ; occupying the penetrating connective tissue and 

 surrounding the lacunae or tubules of the gland, and in many places separating the 

 capillary network from the alveolus or tubule, so that the interchange between the 

 blood and the secreting cells of the part must be carried on through this lymph- 

 space or lacuna. Closely allied to mis is the mode of origin of lymphatics in 

 perivascular and perineural spaces. Sometimes a minute artery may be seen to be 

 ensheathed for a certain distance by a lymphatic capillary vessel, which is 

 often many times wider than a blood-capillary. These are known as perivascular 

 lymphatics. 



Terminations of Lymphatics. The lymphatics, including the lacteals, discharge 

 their contents into the veins at two points ; namely, at the angles of junction 

 of the subclavian and internal jugular veins : on the left side by means of the 

 thoracic duct, and on the right side by the right lymphatic duct. (See description 

 of lymphatics on page 623.) 



Lymphatic glands (conglobate glands) are small oval or bean-shaped bodies, 

 situated in the course of lymphatic and lacteal vessels, so that the lymph and chyle 

 pass through them on their way to the blood. They generally present on one 

 side a slight depression the hilum through which the blood-Vessels enter and 

 leave the interior. The efferent lymphatic vessel also emerges from the gland at 

 this spot, while the afferent vessels enter the organ at different parts of the 

 periphery. On section (Fig. 673), a lymphatic gland displays two different struc- 

 tures: an external, of lighter color the cortical; and an internal, darker the 

 medullary. The cortical structure does not form a complete investment, but is 

 deficient at the hilum, where the medullary portion reaches the surface of the 

 gland; so that the efferent vessel is derived directly from the medullary structure, 

 while the afferent vessels empty themselves into the cortical substance. 



Lymphatic glands consist of (1) a fibrous envelope, or capsule, from which a 

 framework of processes (trabeculce) proceed inward, dividing the gland into open 

 spaces (alveoli) freely communicating with each other ; (2) a quantity of lymphoid 

 tissue occupying these spaces without completely filling them ; (3) a free supply 

 of blood-vessels, which are supported on the trabeculse ; and (4) the afferent and 

 efferent vessels. Little is known of the nerves, though Kolliker describes some 

 fine nervous filaments passing into the hilum. 



1 Atlas of Histology, pi. viii. fig. xiv. 



2 The resemblance between lymph and serum led Hewson long ago to regard the serous cavities 

 as sacs into which the lymphatics" open. Recent microscopic discoveries confirm this opinion in a 

 very interesting manner. 



