Siibcntaneons Vessels in Tail of Lepisosteus 63 



The following observations have been made from a series of trans- 

 verse sections through the tail region of a 90 mm. L. osseus: As shown 

 by Fig. 10, c, there is a conspicuous connecting vessel uniting the right 

 lateral with the right haemal trunk. This communication, which is 

 cephalad of the origin of sinus (x), was not noticed on the opposite 

 side of this series or in any of the gross dissections. In Fig. 13, the 

 left lateral trunk is seen in section uniting with the left sinus (x). 

 Fig. 21 is drawn from a portion of the same section as Fig. 10, showing 

 the right lateral trunk and its communication (c) with the right 

 haemal trunk, greatly magnified. From this diagram it will be seen that 

 the lateral trunk of a 90 mm. L. osseus lies imbedded in a mass of 

 connective tissue directly mesad of the ramus lateralis vagi. Both the 

 lateral trunk and its communicating vessel (c) are composed of a single 

 layer of endothelium, and at the point of anastomosis is a mass of 

 plasma and corpuscles; of these corpuscles the red greatly outnumber 

 the white. The communicating vessel (c) is joined to the body myo'- 

 tomes by a very dense layer of fibrous connective tissue (F. Con. T.). 



Fig. 25 is from part of a section taken through the lateral trunk of 

 an adult L. osseus as seen with a high-power objective. When compared 

 with Fig 21, it will be found to be almost identical in structure. Inter- 

 nally it consists of a layer of endothelium (End.), which is attached 

 externally to a layer of fibrous connective tissue (F. Con. T.), and, as 

 was the case with the 90 mm. specimen, the red corpuscles greatly 

 predominate. 



In Lepisosteus the lateral trunk has a most remarkable size. Its 

 diameter exceeds that of the caudal vein plus the caudal artery, and it 

 maintains this caliber throughout its entire lengih. Since it is in 

 connection with veins at either end, the flow of lymph or blood, which- 

 ever it may be, can pass in either direction. The resistance should be 

 about the same, unless the movement of the tail favored the forward 

 movement. 



Except for its caudal termination, the distribution of the lateral 

 trunk in Lepisosteus is not notably different from other fishes, especially 

 Amiatus, but instead of emptying into the caudal sinus after making its 

 posterior-mesal bend as in Amiatus, it first empties into what has been 

 designated as sinus (x), which has already been described as also 

 receiving the haemal trunk, and sometimes the dorsal trunk, before 

 culminating in the caudal sinus. In Lepisosteus there is never any 

 connection between the lateral trunk and the posterior part of the 



