iV^o.2.1 SHUFELDT ON NORTH AMERICAN TETRAONID^. 335 



very few differeuces worthy of record. In Ortyx and Lopliortiix there 

 are but four caudal vertebrjE and the vomer is markedly acute and long. 

 Occasionally the last segment is but feebly developed, as in Lagopusy 

 where it may be a mere nodule; and in Bonam, too, sometimes a sixth 

 vertebra can be found, but usually requires force to detach it from the 

 pygostyle, and in our specimens seems to be one of those that originally 

 formed that bone — though we do not deny in the face of such evidence 

 that specimens of the Eufled Grouse may be found that possess six of 

 these verlebrte. 



Of tlie Scairular Arch and the pectoral limb. — This arch, with its con- 

 comitant, could have, with all propriety, been described in connection 

 with its vertebra, but so distinct has it become, and so far removed in 

 order to assist in carrying out such a notorious function as the bird's 

 flight, that the author prefers to follow the general ruling of others by 

 discussing it separately. jSTothing could be more entertaining in the 

 ■whole range of osteological research and study than the contemplation 

 of the various avian shoulder girdles with their attached wing bones, 

 particularly the former, as exemplifying the law of equilibrium between 

 a bird's habits, the never-varying part it is to play in nature, and its 

 skeleton or the framework that has been given it to carry that part out. 

 This thought invariably enforces itself upon me in every instance after 

 an examination of a collection of clavicles of different species of birds. 

 It seems that there could not be an equipoise established anywhere in 

 living nature more thoroughly compensatory than that 'twixt a bird's 

 power and mode of flight, and its scapular arch and other bones about 

 the chest — to meet it, more essentially the clavicles. See the broad, ex- 

 cessively pneumatic, yet robust, clavicular arch in any of the genus Ca- 

 thartcs, birds that sail aloft for hours a])i>arently without fatigue, or the 

 very simularly shaped arch in the Canada Goose, but in the latter for 

 a very opposite style of sustained flight is non-pneumatic ; the feeble 

 and often ununited arch in SpheotytOj a bird with scarcely any preten- 

 tions to being a good flyer at all ; in short one would, having a thorough 

 knowledge of a bird's habits, be, in the vast majority of instances, able 

 to guess very near as to the pattern of the furculum he would expect to 

 find. 



Now we have seen, in reviewing the skeletons of the Grouse, that in 

 many i^oints some of the species, if we disregard size, simulate each 

 other very closely, as for instance in the various sterni and vertebrae. 

 The clavicles of these birds form no exception to this rule, as far as 

 general appearance goes. The common model is seen in Plate XII, Fig. 

 87, Cupidonia; but observe even here in these closely-related fowls how 

 habit still tells upon skeletal characteristics. The broad, and not deep, 

 imeumatic U-arch of LkUhartes becomes the long non-pneumatic, almost 

 acute, V-arch of the birds we are describing ; so, in view of being 

 familiar with the habits of the Sharp-ta'led Grouse and Sage Cock, 

 need one be surprised to hud in the fourchette of the flrst a depth of i 



