PALINURUS OR THE SPINY LOBSTER OF BOMBAY. 375 



In this sinus lies the heart, which will be found beating for some 

 time in a recently killed animal. Its walls are thick, muscular 

 and perforated by three pairs of openings, the ostia (Latin, ostium, 

 a door), guarded by valves that admit the blood from the 

 pericardium, but do not allow it to flow back when the heart con- 

 tracts. Two of these ostia can be seen on the dorsum of the heart, 

 the others are on the lateral and ventral aspects and can be seen 

 better on further dissection. 



If desired the blood vessels may be injected with thin plaster of Paris 

 coloured with Prussian blue, or carmine, inserting the nozzle of the 

 syringe into one of the ostia. The injection should be done slowly. 



From the front of the heart a median ophthalmic artery is seen to 

 run forward over the stomach to supply the ophthalmites and anterior 

 part of the head. On each side of the ophthalmic is an antennary 

 artery which passes forward to supply the green gland, antennae, 

 antennules, etc., of its own side. A little below and external to the 

 antennary arteries are the pair of hepatic arteries which supply the 

 digestive gland. Posteriorly the heart gives off a single large 

 median vessel which almost immediately divides into a large dorsal 

 abdominal artery which runs backwards above the intestine to 

 supply it and the dorsal muscles, and a median sternal artery 

 which runs directly downwards, sometimes to the right, more often 

 to the left of the hind gut, to enter the sternal canal, and after 

 passing through an opening in the large thoracic ganglion, divides 

 into two branches, one to run forward below the nerve cord and give 

 off branches to the legs, jaws and neighbouring structures ; the other 

 to run directly backward beneath the nerve cord and supply the 

 abdominal appendages and ventral muscles. 



All these arteries divide in the tissues they supply into smaller and 

 smaller arteries till finally they become capillaries (Latin, capillares, 

 hair-like) microscopic in size. 



In the Vertebrates, as you are aware, the capillaries unite to form 

 small veins, which by further union become progressively larger and 

 return the blood to the heart. In the Crustacean this is not the case, 

 the capillaries terminate by open mouths and allow the blood to pass 

 into large spaces between the viscera and muscles, known as blood- 

 sinuses (Latin sinus, a fold of a garment, a pouch or a bag). These 

 inuses all eventually communicate with a large median longitudinal 



