Observations on the Anatomy of the Sloth. 505 



humeral and femoral arteries in these animals, (vid. Philos. 

 Trans. Lond. 1800,) had excited our curiosity, and prepared us 

 for disappointment ; for after the most careful examination of 

 the arteries, we were unable to detect any resemblance to this 

 rete mirab'de structure, which was thought to explain the cause 

 of the tardigrade movements of the Sloths ; after considerable 

 difficulty in distinguishing the nerves from the arteries, (the ac- 

 tion of the spirits had rendered them similar in appearance,) we 

 only succeeded in detecting and passing probes into the cavities 

 of the humeral profundal, and the radial, ulnar, and interosseal 

 branches at the elbow ; but as the present specimen had been 

 preserved in spirits, and Mr. Carlisle injected the arteries of his 

 specimen, we are not authorized to question the observations 

 of so accurate an observer, from the results of a single dissection. 

 We wish, however, to direct the attention of comparative anato- 

 mists who may possess an opportunity, to a re-examination of 

 this arterial arrangement. 



It will be apparent, from what we have said, that the term 

 Tardigrade, derived from the extreme slow ness of this animal, 

 does not express its principal character ; that the peculiar or- 

 ganization of the Bradypus, and its prodigiously compressed and 

 crooked nailsf cause its locomotion upon the surface of the 

 ground, to be very slow, is true ; but if one animal existing un- 

 der this negative condition, is to be called Tardigrade, we con- 

 ceive that all animals under like restraint, and not belonging to 

 the Edentata, may, with equal propriety, be put among the 

 Tardigrades. 



The mud-fish of the genus Hydrargira of Lacepede, are often, 

 by the retreat of the tide, left on the shore. These animals have 

 the faculty of springing up and changing their place ; they will 

 thus advance over a considerable space, until they gain the 

 water, which is their proper element. In like manner, the 

 Bradypus, by an imperfect motion when on the surface, gains 

 the trees where it lives, feeds, and sleeps. It rarely leaves the 

 tree it is on until it has stripped it of every leaf, so painful is 

 the effort to change its situation, by dragging itself on its elbows 

 from one tree to another when they stand far apart. The nails of 

 this animal, when at rest, are always bent towards the palm of 

 the hand; and it is thus it sleeps, grasping the branches, and 

 suspended with its back towards the ground. We think the 



Vol. I.— 64 



