732 TEE LYMPHATICS IN PARTICULAB. 



" It usually opens at the junction of the jugulars, at the side of the vessels, by 

 an orifice furnished with a double semilunar valve. Sometimes one or two of 

 the branches which coucar to form it, describe circumvolutions around the 

 corresponding brachial trunks or some of its divisions, before joining the others. 

 Lastly, it is not rare to see this lymphatic trunk anastomose with the thoracic 

 duct by voluminous collateral branches, then unite with it in such a way as to 

 be inserted together by a single orifice above the confluent of the jugulars " 

 (Colin) 



Differential Characters in the Lymphatic System of other than Soliped Animals. 



Tlie lymphatic system, glands and vessels, is more developed in Kuminants and the Pig 

 than in the Carnivora. 



In this respuct the domesticated animals may be classified in the following order : Ox, 

 Sheep, Horse, Pig, Dog, Cat. 



Ruminants. — " The thoracic duct of large Ruminants, wlien it has entered the thorax by 

 a special opening in the diaphragm, almost distinct from tliai of the aortic hiatus, is placed 

 above and to the light of the aorta, between it and the spine. There, although outside the 

 eorrespDnding intercostal arteries, it is completely concealed by a thick layer of adipose tissue, 

 in which are numerous subdorsal glands. Towards the fifth dorsal vertebrr., it receives a large 

 lymphatic vessel from the enormous gland on the track of the oesophagus in the posterior 

 mediastinum ; it then crosses the direction of the aorta and the cesoi)hagus, passes to the left, 

 gains entrance to the thorax, and opens in front of the first rib, above the junction of the left 

 jugular with the anterior vena cava." ' 



" The varieties it presents in the Ox are numerous and very common. The rarest dis- 

 position is that of a canal, single throughout its 

 Fig. 402. entire length, such as it has been described, and 



such as it is usually found to be in small Ruminants 

 (Fig. 406). This canal (Fig. 403), single at its 

 origin and for the greater part of its extent, often 

 bifurcates towards the base of the heart, or at a 

 short distance from its insertion. Of these two 

 branches, one passes to the rigiit of the oesophagus 

 and trachea, the other to the left of the^e, in follow- 

 ing the ordinary direction; and, at the entrance 

 to the thorax, they either terminate separately, each 

 entrance of the thoracic duct in in the angle formed by the union of the jugular and 

 THE ox. corresponding axillary vein, or together at the samo 



point — the confluent of the two jugular veins. 

 "It happens tliat one of the branches of the bifurcated canal is, in its turn, subdivided Into 

 two smaller branches, and that the other experiences at the same time a similar subdivision; 

 so that the trunk of the canal, at first single, becomes double, then quadruple, and consequently 

 opens into the venous system by four distinct orifices. If the branches of tiie canal, instead of 

 remaining isolated, send oflT transverse anastomoses, there results a complicatioa of which 

 Solipeds do not offer an example (Fig. 402). 



" The tlioracic duct is often double throughout its extent. The two canals are then detached 

 separately from the receptaculum chyli; one follows the right side, the other the left side of 

 the aorta, describing an arcli with concavity downward at the base of the heart, on the lateral 

 parts of the trachea, terminating either very near one another, and on the same transverse line, 

 at the junction of the two jugulars ; or one to the right, the other to tiie left, in each of these 

 two veins, ard not far from their junction with the axillarns (Fig. 404). 



" Wiien the two canals arise from the receptaculum, tiiey sometimes repeatedly anastomose 

 with each other by sinuous and curved branches, as shown in Fig. 405. 



" Then all the branches collect in the anterior mediastinum, and constitute a single canal 



(' Zundel has pointed out the curious fact, that in Ruminants, the long, special, lymphatic 

 gland situated between the layers of mediastinum and above the oesophagus, sometimes becomes 

 80 voluminous that its weight impedes rumination, especially when the animal is lying. The 

 bolus of food is prevented from ascending into the oesophagus, and this may become a frequent 

 and periodic cause of indigestion.) 



