WHITE SHRIMP FROM THE GULF OF MEXICO 



143 



branch is the subgastric artery (fig. 79) and it 

 runs around the posterior end of the gastric mill 

 to a curious glandlike organ lying beneath the 

 gastric mill. The subgastric artery is similar to 

 the internal ramus of the lateral anterior artery 

 described by Baumann (1919) in Astacus. Ros- 

 trad of the subgastric branch, the lateral anterior 

 artery puts out the dorsal gastric artery (tigs. 79, 

 80) which serves the dorsal regions of the gastric- 

 mill. The gastric artery, too, divides into at least 

 three major divisions (fig. 80). one running some 

 distance rostrally, another caudad into a gland- 

 like structure of unknown function (see fig. 79, 

 dorsal gland, and a third passing around the 

 gastric mill ventrally. 



The lateral anterior artery now turns to the 

 midline, to join its counterpart from the opposite 

 side. The optic artery continues anteriorly to the 

 eyestalk from this turn, giving off a branch, the 

 cerebral artery, to the supraesophageal ganglion. 

 At the midline, the two lateral anterior arteries 

 form a median longitudinal vessel. The anterior 

 portion extends into the rostrum while the poste- 

 rior part, the recurrent artery, runs caudad to the 

 dorsal surface of the gastric mill. At the junction 

 of the optic artery with the oculomotor, a small 

 branch is given off which runs beneath the optic 

 tract and thence to the midline to meet its op- 

 posite number from the other side (fig. 80) slight- 

 ly rostrad of the dorsal brain. No evidence of the 

 frontal heart so prominent in this region in other 

 decapods (Baumann 1917) has been found in 

 Penaeus. 



The next major branch of the lateral anterior 

 artery anterior to the gastric branch is the man- 

 dibular artery. Upon leaving the lateral anterior 

 artery this branch passes between the lateral man- 

 dibular condyle and the origin of the lateral an- 

 terior thoracic muscle 1 (fig. 80) into the sub- 

 stance of the mandibular muscles where the vessel 

 undergoes further subdivision. 



Rostrad of the mandibular artery, the lateral 

 anterior artery gives off the large antennal artery 

 whose subdivisions include a branch to the anten- 

 nule. The major portion of the antennal artery 

 leads to the muscles and other organs of the 

 antenna. 



HEPATIC ARTERY 



Running from the heart is another pair of 

 arteries, the hepatic arteries (fig. 79). These 

 project from the anteroventral surface of the 



heart and run into the hepatopancreas. They are 

 difficult to follow within the gland in preserved 

 material because of postmortem effects. 



DORSAL ABDOMINAL ARTERY 



The largest artery passing from the broad, 

 posterior end of the heart is the unpaired dorsal 

 abdominal artery (figs. 61, 62, 79, 80). This 

 vessel runs the length of the abdomen between the 

 dorsal abdominal muscles and the gut. As it pro- 

 ceeds caudad, the dorsal abdominal artery gives 

 off pairs of segmental arteries at each segmental 

 junction (Hg. 62). In addition, numerous small 

 vessels from the dorsal abdominal artery irrigate 

 the gut throughout its length. Posteriorly, the 

 dorsal abdominal artery bifurcates around the 

 hindgut gland (tig. 82) and runs alongside the 

 rectum as a paired vessel. In the neighborhood 

 of the rectum the paired vessels turn ventrad, 

 after giving several branches to various structures 

 of the region, including the telson. and anasto- 

 mose beneath the posterior part of the rectum. 

 Having fused, the vessel passes caudad of the 

 ganglion of the sixth abdominal segment and then 

 turns anteriorly as the posterior subneural artery 

 (tigs. 81, 82). So far as can be determined, the 

 posterior subneural artery extends no further 

 rostrad than the anteroventral part of the sixth 

 abdominal segment. 



On the dorsal surface, the segmental arteries 

 give off branches adjacent to the dorsal abdominal 

 artery (fig. 62). These branches enter the large 

 ventral abdominal muscles. The remainder of the 

 segmental arteries now pass ventrally along the 

 lateral surface of the abdomen at the interseg- 

 mental lines. A substantial branch splits off 

 internally and runs across the external arm of 

 the anterior oblique muscle in each segment (fig. 

 60). The segmental artery (see lateral artery, 

 fig. 81) continues ventrad between the abdominal 

 muscles and the promoter-remotor muscle mass 

 of the pleopod and sends a branch, the pleopod 

 artery, into the pleopod (fig. 81). A second 

 branch proceeds into the substance of the abdom- 

 inal ganglion. This branch also divides again to 

 form the postganglionic loop (fig. 81) which pro- 

 vides a vascular connection between the segmental 

 arteries of both sides. 



STERNAL ARTERY 



In general, the ventral vascular supply is less 

 distinctly laid out than are the dorsal circulatory 



