THE EIGHT THOBACIC DUCT. o65 



during digestion, mixed lymph and chyle— into the V. jiigularis 

 externa. 



The duct almost invariably divides into two or more trunks near 

 the middle of its course. After extending for a few centimeters as a 

 double or triple duct, it may unite and then divide again before 

 emptying into the vein (Fig. 103). See Colin, A, article Thoracic 

 Duct., for variations in the domestic animals. 



§ 989. Dissection.— Slit the diaphragm ventrad from the hiatus 

 aorticus (Fig. 90), and turn the two crura or pillars of the dia- 

 phragm aside as shown in Fig. 103, Crus dphrg. Turn the heart 

 and lungs to the right, and, if the cat is lean, the thoracic duct will 

 be seen on the dorso-sinistral side of the aorta, as a continuation 

 cephalad of the receptaculum (Fig. 103). Cephalad of the heart it 

 rests on the ventral aspect of the A. subclama sinistra. It finally 

 crosses the V. hrachiO'Cephalica sinistra and, receiving the vasa 

 lymphatica from the head and neck, empties into the V. jugu- 

 laris externa near the angle of union of tliat vessel with the V. 

 subclama. As a rule, however, the thoracic duct opens into the 

 vein in two places, as shown in Fig. 103. Both branches of the 

 divided thoracic duct may receive a lymphatic vessel from the head 

 and neck. In isolating the duct, it is necessary to proceed with 

 great care. The tracer must be employed sparingly. The pleura 

 and connective tissue are most safely removed piecemeal with scis- 

 sors and fine forceps, as directed for exposing the nerves and sali- 

 vary glands of the face (§ 777). It is especially difficult to isolate 

 the duct in its cephalic third, as it is usually double or triple, and 

 each part therefore correspondingly small (Fig. 103, A). 



The first rib must now be carefully cut and removed. Tlie 

 largest of the vasa lymphatica in the neck rests on the longus colli 

 muscle entad of and parallel with the carotid artery. 



§ 990. Ductus thoracicus dexter. — The right thoracic duct or 

 great lymphatic win is the large lymphatic trunk into which empty 

 the vasa lymphatica of the right side, of the thorax, of the head and 

 of the neck. It opens into the right Y. jugular is externa in the 

 same way as the left empties into the left Y. jugularis externa. 



% 991. Exposure and Dissection. — Employ the same specimen 

 that was used for the left duct, make an incision on the right along 

 the neck, and expose the Y. jugularis externa to its junction with 

 the V. subclavia. Do this veiy carefully. The vasa chylifera will 

 be seen dorsad of the aorta, and entering the veins as described after 



