193 The Development of the Lymphatics iu the Skin 



Callum/ The original discovery of this method of growth was made, 

 not by Eauvier, as I stated in a previous paper, but by Langer* in 1868. 

 At the time of my first publication I had not seen Langer's paper. He 

 published a series of papers on the lymphatic system of the frog, and in 

 one of them on the lymph vessels in the tadpole's tail, he gives beautiful 

 pictures of the lymphatics, with their complete lining of endothelium 

 and with the long sprouts of endothelial cells from their walls. Some 

 of the sprouts he shows as still solid, others partly injected. He recog- 

 nized that this represents the method of growth; moreover, he states that 

 without doubt the lymph capillaries and the blood capillaries develop in 

 the same way — their elements being the same. 



The plexus of growing lymphatics is well seen when the freshly in- 

 jected skin of the embryo pig is stripped off and examined under a 

 binocular microscope. It can thus be made out that the ducts spread 

 out practically in one plane. 



By the time the pig is 8 cm. long an injection of the lymphatics shows 

 the primary plexus well developed. Many of the vessels are large and 

 the plexus is wide meshed. At the same time the skin viewed under the 

 binocular shows that there are numerous sprbuts from the primary 

 plexus which are growing outward into the chorium. These small, new 

 sprouts do not as yet make a perfect plexus within the chorium. Sec- 

 tions of the skin at this stage bring out three points: First, that the 

 ducts of the primary plexus now lie deeper in the subcutaneous tissue 

 rather than just in the border between the subcutaneous tissue and the 

 chorium. Secondly, that there are a few lymphatic vessels within the 

 chorium; and, thirdly, that the blood capillaries are nearer the surface 

 of the skin than the lymphatics. 



By the time the pig is 10 or 11 cm. long the lymphatic capillaries 

 within the chorium have become a complete plexus. Viewed under the 

 binocular microscope, there are now two distinct layers of lymphatics, 

 a deeper plexus with wide spaces between the ducts and a more super- 

 ficial plexus of finer ducts more closely crowded together. In sections 

 the deeper plexus is subcutaneous, while the superficial lies about the 

 middle of the chorium. The complexity of the plexus varies greatly in 

 different parts of the body, for example, there are many more lymphatics 

 in the ear than in an area of skin of equal size over the back. The 

 stages of development are given for the skin over the shoulder, the 



'MacCallum: Arch. f. Anat. u. Phys., Anat. Abth., 1902. 

 ■■Langer: Die Lymphgefasse im Schwanze der Batrachier-Larven. Sitzb. 

 d. k. Akad. d. Wissensch., I. Abth., Juli Heft, Jahrg. 1868. 



