The intestinal trunk (Figure 24: 13, 13) is a large lymph vessel, which originates near the cranial mesenteric artery from the confluence of the efferent vessels of the middle and right colic lymph nodes, the splenic lymph nodes (Figure 24: 3, 3’), the left hepatic lymph node (Figure 24: 2), the right hepatic lymph nodes (Figure 24: 1), the jejunal lymph nodes (Figure 24: 4, 41, 42, 43), and the more cranially located lumbar aortic lymph nodes (Figure 24: 5), including the cranial lumbar aortic lymph node (Figure 24: 6).
The intestinal trunk travels upwards on the right side of the cranial mesenteric artery (Figure 24: p), but may be slightly cranial and to the right of it, and opens into approximately the middle of the cisterna chyli (Figure 24: 12). The confluence of these efferent vessels into the intestinal trunk is not clearly defined because of the extensive network formation by the efferent vessels (see following).
In some cases, the intestinal trunk may be doubled or even tripled, or individual lymph vessels of the aforementioned network may open separately into the cisterna chyli (as in Figure 24), and there may even be no distinct intestinal trunk(s) at all, instead, several thicker vessels of varying sizes emerge from the extensive network of the efferent vessels of the jejunal lymph nodes, middle and right colic lymph nodes, splenic lymph nodes, etc. (the rete intestinale or intestinal network) and open separately into the cisterna chyli. These thicker vessels emerging from the extensive network of efferent vessels enter the cisterna chyli at different points; they may first either cross over the left or right side of the aorta and sink in the dorsal wall of the cisterna chyli.
The aforementioned intestinal network frequently extends very close to the cisterna chyli, often so close to it that the small lymphatic trunks leaving the network and opening into the cisterna chyli are very short. The aorta may in fact even be wrapped in a network of lymph vessels.
Since the efferent vessels of the lymph nodes mentioned above are connected in a network, it was noted that when the efferent vessels of one of the lymph nodes are filled, the efferent vessels of the other lymph nodes fill in a retrograde manner; this occurs to a greater extent if the outflow of the lymph is impeded for any reason: i.e. if congestion of this portion of the lymphatic system occurs, lymph from one of the lymph nodes (e.g. a jejunal lymph node) can then flow to all the other lymph nodes (the right and middle colic lymph nodes, hepatic lymph nodes, splenic lymph nodes, and other jejunal lymph nodes).