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artery. Immediately on leaving the heart it dips down- 

 ward and makes an outward sweep in the deeper parts of 

 the digestive gland. Near its origin on its inner side it 

 gives oft' a branch which goes to the hind-gut. There are 

 also other small branches which supply various parts of 

 the gland. The main artery, however, divides into two 

 branches, the posterior of which sweeps outward em- 

 bedded in the posterior part of the digestive gland. '1 In- 

 anterior branch passes beneath the goiiad and the 

 external adductor muscle of the mandible and supplies 

 the anterior portion of the gland. 



Posterior aorta (Superior abdominal artery) (PI. 

 VIII, fig. 51, PL IX, fig. 53, s. art.). This arises as a 

 median vessel from the posterior end of the heart. Just 

 after leaving the heart it gives off at each side a small 

 vessel. This passes forward and downward beneath the 

 pericardium, and supplies those parts of the reproductive 

 organs lying beneath the pericardium, and also some of 

 the muscles of the Basi-Ischium of the Chela. 



Immediately above the hind-gut caecum a second 

 pair of branches arises. These are the Postero-lateral 

 arteries (pi. art.), and have several complicated branches. 

 The main branch passes outwards above the coils of the 

 caecum and divides into two vessels. The anterior vessel 

 passes forward and gives off branches to the extensor 

 muscles of the coxopodites of the four walking legs. The 

 posterior branch supplies the muscles extending from the 

 " flancs " to the carapace, and also gives a rich blood 

 supply to the coils of the hind-gut caecum. 



Behind the origin of the postero-lateral arteries the 

 posterior aorta enters the abdomen. As the arrangement 

 in the two sexes is somewhat different, these will be 

 described separately. 



Female. The aorta passes down the abdomen 



