1904.] CIUCrivATORY SYSTEM IN THE OPIIIDIA. 339 



Furthermore, this right aortic ai'ch is a much more delicate vessel 

 than the left aortic arch, which it joins at a point about 10 mm. 

 behind the heart. Just after leaving the common trunk the 

 right aortic arch is crossed superficially by the vertebral vein. 

 The latter is formed of two branches, which emerge from the 

 thickness of the parietes in the middle line and join before crossing 

 the aorta as a single trunk. 



Neither the right nor the left aortic arch gives oft' any branches 

 to the parietes before their union. In the male specimen, how- 

 ever, there were two such branches. The origin of the anterior 

 vertebrcd artery has been already described. It rapidly ascends to 

 the median dorsal line and is lost to sight, becoming imbedded in 

 the neck 2 inches in front of the heart and 5^ inches behind the 

 tip of the snout. It gives off no backwardly running superficial 

 posterior vertebral artery as in Python spiloies, but a number of 

 intercostals plunging at once into the thickness of the parietes in 

 the dorsal middle line arise from it. Of these the first is 5 mm. 

 from the junction with the right aortic arch, the next 10 mm. 

 from the first, and the third 18 mm. farther towards the head 

 than the second — i. e., three 'in all. It also gives ofi"a number of 

 small branches to the oesophagus, which I do not further particu- 

 larise. In the second individual there were also three intercostals 

 given off from the antei-ior vertebral artery. It is important to 

 note that this anterior set of intercostals plunge into the parietes 

 exactly in the middle line. 



The single aorta is not increased in calibi-e at the junction and 

 passes back in a more or less straight line ; it gives off" a very 

 large number of branches, of which the following is, I trust, an 

 accurate account. 



There is, in the first place, a series of impaired intercostal 

 arteries which pierce the parietes along the middle line of the back. 

 Most of these arteries are slightly convoluted, so as to allow of 

 stretching. The first two are at regular intervals of 30 mm. from 

 each other or from the junction of the aortse ; the third arises 

 further away, 40 mm. or so from the second. Closely associated 

 with this is the first of a series of veins emerging from the parietes 

 in a similar fashion, which will be dealt with shortly. The 

 distances separating the origins of the next six branches are 35, 

 25, 25, 30, 40, and 30 mm. respectively; the 10th is only 10 mm. 

 from the 9th. 



The next two complete a series of 12 intercostals, all of which 

 enter the parietes on the left side of the median dorsal line. 

 After this point there is a more or less regular alternation in the 

 point of entrance into the parietes ; some of the arteries pierce 

 the body on the right, some on the left. A few, moreover, are 

 strictly paired, and each artery of the pair pierces the parietes 

 either on the right or on the left. There were three such pairs 

 in the specimen examined, all of them towards the end of the 

 series. The total number of arteries which I counted was 46. 

 I do not paTticularise, since they differed somewhat in the second 



'79* 



