TISSUES OF THE BODY. 379 



Koelliker tells us that twigs of only 0*2256-2609 mm. may be pos- 

 sessed of three tunics. Around the cellular coat a longitudinally fibril- 

 lated elastic membrane is to be found, as serosa, then a media consisting 

 of contractile fibre cells and elastic fibres, which is covered by an 

 adventitia of longitudinal fibrous tissue. 



Fig. 382. Lymphatics from between the longitudinal and transverse layers of muscle in the 

 small intestine of the Guinea-pig, c, fine, and d, larger canals; ab, plexus myentericus of 

 Auerbach. 



In still larger absorbent vessels the structure is similar. They corre- 

 spond in this respect with the veins, as is well known. 



In the thoracic duct the epithelium presents itself enclosed in several 

 layers of fibrous membranes, upon which an elastic network is laid down, 

 its elongated meshes arranged in the long axis of the vessel. The next 

 or middle coat consists of connective-tissue, coursing with its fibres 

 in the direction of the tube, after which we come upon transverse 

 muscular fibres. The adventitia presents for our consideration, besides 

 ordinary connective-tissue, scattered bundles of unstriped muscle arranged 

 in a reticular manner. According to Koelliker. the serosa has a thickness 

 of hardly 0-0135-0-0226, and the media of 0-0564 mm. 



The relations of these canals to the lymphatic glands, on their arrival 

 in the latter, we reserve for the third part of our work. 



REMAKKS. (1.) Teichmann was of opinion that the foundation of the whole lym- 

 phatic system consisted of structures resembling stellate cells (Saugaderzellen). He 

 regarded them as metamorphosed cells which had preserved their envelope, and 

 which, united through their processes, thus formed the "lymphatic capillaries." (2.) 

 Among the views in question great variety may be observed. Many have simply 

 accepted the membraneless interstices of interstitial or other connective tissue as the 

 commencement of the absorbent system. The extensibility of this tissue was sup- 

 posed to lead to the formation of clefts or openings into the neighbouring parts on 

 increased pressure, artificial or natural (Briicke and Ludwig). Recklinghausen, in his 

 article "Die Lymphgefasse und ihre Beziehung zum Bindegewebe," Berlin, 1862, 

 appears to have arrived at peculiar results in his investigations. According to him 

 (and the merit of the discovery rests with him), all lymphatic radicles are clothed 

 with that epithelium already mentioned. They are, however, says he, related to 

 those formations of connective-tissue so well known from Virchow's works as con- 



