20 Prof. BucKLAND on the Adaptation of the Structure 



peculiarity tiiat occurs in almost eveiy bone of the skeleton, and these of course 

 corresponding with peculiar structures in the muscles and soft parts of the 

 animal*. Cuvier observes with respect to the articulation of the hind-feet, 

 that it seems contrived expressly to deprive the animal of the power of using 

 them in the act of walking ; that whereas, in most animals, the articulation of 

 the ankle with the leg is effected by a hinge more or less pliant, which permits 

 the foot to play upon the leg upwards and downwards, in the Sloth a pointed 

 pivot at the bottom of the small bone only of the leg, enters a conical cavity on 

 the upper surface of the astragalus or chief bone of the instep, rendering it 

 impossible for the foot to move vertically in the ordinary manner, and allow- 

 ing it only to turn horizontally upon the pointed pivot : it follows further, that 

 the sole of the foot is in the same vertical direction with the bone of the leg, so 



* Sir Anthony Carlisle, in a paper published in the Philosophical Transactions, 1800, notices a pe- 

 culiarity in the arteries of the limbs of slowly moving animals. The axillary and iliac arteries which 

 are distributed on the muscles of the upper and lower limbs, are suddenly divided at their entrance to 

 these limbs into a number of equal-sized cylinders, which occasionally anastomose with each other, 

 and are exclusively distributed on the muscles of the limbs, whilst the arteries of all other parts of the 

 body divide in the usual arborescent form. He first observed this structure in the Macauco (Lemur 

 tardigradus, Linn.), and subsequently found a similar distribution of the arteries of the limbs in two 

 species of Sloth ; in the Bradypus tridactt/lus he counted 42 separate cylinders on the surface of the 

 brachial fasciculus, besides about 20 more, which were concealed within ; he found 34 similar branches 

 in the middle of the thigh. In the Bradypus didactylus, whose movements are quicker than those of 

 the B. tridactylus, he found a similar distribution of the arteries, but to a less degree. As the eflfect 

 of this subdivision of the arteries is to retard the velocity of the blood passing to the muscles of the 

 limbs, he points out the importance of these phenomena in relation to the physiological question, 

 " whether the slow movement of the blood sent to these muscles be a subordinate convenience to 

 other primary causes of their slow contraction, or whether it be of itself the immediate and principal 

 cause." 



Sir Anthony Carlisle also notices the existence of an analogous arrangement of blood-vessels in the 

 carotid artery of the Lion, and suggests, that this peculiarity may be subservient to the long-continued 

 exertion of the muscles of his jaws whilst holding a powerful animal, such as a Horse or Buffalo, and 

 thus enable him to retain his prey. 



Kircher in his Musurgia states that he received a description of the Sloth from Father Torus, Pro- 

 vincial of the Jesuits in America, who had animals of this kind in his possession, and made many 

 experiments in relation to their nature and qualities. He put a long pole under the feet of one, which 

 it seized upon very firmly, and would not let go again : the animal thus voluntarily suspended was 

 placed between two beams along with the pole, and there it remained without meat, drink or sleep 

 forty days. At last, being taken down, they let loose a dog on it, which after a little while the Sloth 

 Beized with his feet, and held him four days, till he died of hunger. 



