THE FTERYLOGRAPHY OF THE RUFFED GROUSE 745 



the posterior region. Another set of rows curves up toward the back. Besides covering the 

 thigh, the feathers aid in protecting the side of the abdomen by extending backward to the 

 tail coverts. 



Crural. This tract covers the tibio-tarsus and may be divided into internal and external 

 regions, both of which are similar to and continuous with the femoral tract. The rows are 

 not very definite. The feathers are sparse and present a peculiar appearance, more like fur 

 than feathers. They are possibly of a type which is less subject to wear than the ordinary 

 flat, stiff kind. The feathers of the tarso-metatarsus, although a direct continuation of those 

 of the femoral region, are sometimes considered to make up a separate pedal tract. Thev are 

 most prominent in the more northern subspecies*. 



The Spaces 



As already mentioned, around and between the feather tracts are areas of bare skin called 

 spaces. Although devoid of feather growth'^ they are, in life, covered by the feathers adja- 

 cent to them. Like the tracts, their arrangement is similar on both sides of the body. The 

 following have been recognized. 



Capital. Several areas of this kind are found on the head. The large temporal space is 

 above and in front of the ear. It is covered by feathers on either side and in front. Above 

 the eye is the superciliary space into which folds the upper eyelid. A similar but smaller 

 space is found on the lower eyelid. Ordinarily these two spaces arc not covered by feathers. 

 The rictal space extends over the rear part of the lower jaw ])ciiic on either side. In the 

 middle of the forehead is the frontal space. 



Lateral Cervical. This space begins about inidwa) in the fr<jnt of the neck and extends 

 to a point parallel to the humeral tract. Together the portions on either side of the median 

 line occupy about one-third of the circumference of the neck. In life the area is well cov- 

 ered by feathers from the ventral and dorsal cervical tracts. Its function has been considered 

 to be to provide a space for the shoulders when the neck is folded. Probably another func- 

 tion is to facilitate greater flexibility of the skin since, in other regions of the neck, the 

 skin is noticeably stiffened b) the feather bases. 



Lateral Spaces of the Trunk. These include all the various spaces of the body surround- 

 ing the wings and legs. A few small downy feathers are found scattered throughout. They 

 facilitate freedom of movement and accommodation for the folded wing and bent leg. 



Spinal and Inferior Spaces. These occur along the middle lines of the upper and lower 

 surfaces of the body. Both are relatively small in the ruffed grouse, particularly the spinal 

 space which is quite inconspicuous except at its anterior end. One function of the inferior 

 space is, apparently, to provide a smooth body contour, not only by hiding the projecting 

 breastbone but also by concealing the folded neck. 



Upper and Lower Wing Spaces. Rather indefinite in shape on the upper surface of the 

 wing, the space is the general area outside of the humeral tract which bears a reduced number 

 of small feathers. On the lower wing surface there are several small spaces on either side of 

 the axillary feathers, one of which can be traced out to the hand. Both seem to facilitate 

 folding the wing. 



Crural. Separating the femoral tract from the rest of the plumage, the crural space ap- 

 pears in most birds as a naked ring or the upper region of the tibia. In the ruffed grouse 



* See Chapter H. p. 47. 



A Other studies have ahnwii that many of these spates regularly become covered with down during the winter, (p. 811. 



