682 FOURTH REPORT — 1834. 



and velocity of the blood are rendered equal through the whole 

 series. In speaking of the dii'ection of the vessel, he adverted 

 to the tortuous entrance of the internal carotid and vertebral 

 arteries into the skull in the human subject, and showed that 

 it is still more remarkable in the horse, which in feeding requires 

 to have the head for a considerable time in the dependent pos- 

 ture. But the best examples of the tortuous, or serpentine, 

 course are to be seen in the spermatic arteries of the Mammalia. 

 This mechanism, the author contends, adapts the circulation to 

 the various positions in which organs may be placed, and to 

 their states of action and repose. In speaking of the third mo- 

 dification, or the subdivision into numerous long branches, he 

 particularly alluded to the observations of Sir A. Carlisle with 

 respect to the arteries of the sloth, and showed that a similar 

 ramification is found in the hedgehog, both in the arteries of 

 the panniculus carnosus and of the mesentery. Of the last mo- 

 dification, the plexus, he showed examples in the rete mirabile 

 of Galen in the internal carotid, and of Hovius in the ophthal- 

 mic artery, of the liuminantia. He inferred that this structure 

 prevents valvular turgescence, which would otherwise occur 

 during the long period these animals keep their head in the de- 

 pendent position while browsing. He also showed that a rete 

 mirabile exists in the ophthalmic artery of the seal and goose, 

 and considered it probable that in them it is conducive to the 

 alternate adaptation of the eye to vision in air and water. He 

 described the remarkable plexiform arrangement which exists 

 in the mesenteric arteries and veins of the hog ; and instituted 

 a comparison between those vessels in carnivorous and herbivo- 

 rous 3Iammalia, concluding that these modifications are in con- 

 formity with the transmission of blood through the liver, the 

 rapidity of the peristaltic motion, and the power of nutrition. 



Observations on the Anatomy of the Blood-vessels of the Por- 

 poise. By Dr. Sharpey. 



I. The artery of the anterior extremity or fin of the porpoise, 

 corresponding to the brachial in man, presents a peculiarity of 

 distribution similar to that observed in the arteries of the limbs 

 of slow-moving animals. The vessel, after crossing the first 

 rib, divides into a great many long and small arteries, which 

 run nearly parallel, but repeatedly anastomose, so as to form an 

 elongated plexus, consisting at its thickest part of at least forty 

 vessels. This plexus continues as far as the distal end of the 

 humerus, where its component vessels again unite into five or 

 more larger arteries, which run along the radius and ulna. 



