46 INTRODUCTION. 



8. The iscMo-coccygeus arises from the posterior edge of the 

 ischium, passes laterally along the coccyx, and is inserted be- 

 neath into the edge of the last vertebra, and the adjoining part 

 of the ligamentous fascia. It draws the tail laterally, and 

 tends to depress it. 



4. The pubi-coccygeus arises from the pubes and adjoining 

 part of the ischium, and is inserted into the base of the fascia 

 of the quills. Its action is to bend the tail to a side, and to 

 spread the quills. 



Fig. 6. represents the lower surface of the 

 tail ; the feathers, ^, b, being cut short, and 

 the skin removed. The pubi-coccygeus, 4, 

 is seen in its whole length ; the ischio- 

 coccygeus, 3, is also seen passing over the 

 latter, and inserted into the last vertebra ; 



Fig. 6. Lotoer Surface of . , /» , i i x ^ 



Tail. as IS part ot tne quadratus, z. 



5. The remaining muscle is the depressor coccygis^ which is 

 much more powerful than the levator. It arises from the pos- 

 terior edge of the pelvis beneath, and from the sides of the 

 vertebrae, to be inserted into the inferior spinous processes, and 

 into the sides of the last vertebra. The action of the two 

 muscles is to depress the tail ; but when acting singly it draws 

 it outwards and downwards. 



The feet of birds afford a subject of observation as varied and 

 interesting as the wings ; but as numerous opportunities of 

 describing them will occur in the course of the work, it is un- 

 necessary to treat of them here. They vary in the proportional 

 development of their parts, and even in the number of the toes, 

 as well as in their position and degree of connection or separa- 

 tion, according to the different modes of progression used by 

 the different species. Some birds walk by bringing their feet 

 alternately forward, others by a simultaneous motion of these 

 organs ; some run with great velocity, while others are scarcely 

 able to walk ; some can hardly even stand ; most birds walk 

 only on a flat surface, but some are enabled to ascend a vertical 

 plane ; and many, by having their toes joined by membranes, 

 have their feet converted into paddles, and are thus fitted for 

 advancing on the water. 



