THE SPINAL COLUMN OF QUADRUPEDS. 133 



standing directly behind it, while, at the same 

 time, the body and limbs remain unmoved. As 

 the creature thus embracing and attached to 

 the trunk or branch of a tree can keep no look- 

 out in front, the increased flexibility arising 

 from the position of these two anterior dorsal 

 vertebrse (cervical ?) may be considered as a 

 compensation, enabling it to see and guard 

 against the approach of its enemies, in flank 

 and rear, as well as to see the position of its 

 food. The habits of the sloth are unique among 

 quadrupeds, and so also is this compensation. 

 Another advantage arising frpm this unusual 

 flexibility may be to afford ease to the neck, 

 under the peculiar position Avhich the sloth 

 assumes in taking its repose. In the case of an 

 animal, a great part of whose life, when not 

 engaged in eating, is spent in sleeping on trees, 

 an easy attitude for repose is most essential to 

 its comfortable existence; and, accordingly, we 

 find that the auxiliary vertebrae at the base of 

 the neck contribute to produce that flexibility 

 of this organ which allows the head of the 

 animal to incline forward and rest upon its 

 bosom." 



It is curious to compare the swan-like neck 



