THE ANATOMY OF THE RUFFED GROUSE 725 



verse process and a short thick neural spine. According to Shufeldt'", Gallus and Pedioecetes 

 have six free caudal vertebrae. Tympanuchus has five. 



Ribs. The rib arrangement of Bonasa is typical of the Tetraonidae. There are seven pairs 

 of ribs, including one borne on the last (fifteenth) cervical vertebra and one borne on the 

 first thoracic vertebra, neither of which reach the sternum. The cervical pair are short slivers 

 of bone, while each of the second pair is longer and possesses an uncinate process. The next 

 four are composed of two parts: the dorsal, which articulates by its head with the centrum 

 of the vertebra and by its tuberculum with the diapophysis; and the ventral, which articu- 

 lates with the sternum. All possess an uncinate process loosely joined to the dorsal part. The 

 two parts form a V with the apex directed posteriorly. The seventh and last rib arises from 

 the first vertebra of the synsacrum, but also (as noted above) articulates with a facet on the 

 fifth thoracic vertebra. It also is composed of two parts. The ventral part does not reach 

 the sternum and neither does it have an uncinate process. Tn Trmpnmirhus this sternal rib 

 unites with the sixth rib. 



Sternum. The sternum (figure 77d) possesses the forked lateral xiphoid processes, char- 

 acteristic of the Galliformes, with the thin medial branch extending nearly as far posteriorly 

 as the tip of the sternum. In the median line, at the upper end. lies the manubrium which has 

 a perforation in line with the coracoid groove. The anterior manubrial process is widely sep- 

 arated from the manubrium proper. The ribs attach to the edge of the sternum between the 

 external lateral process and the manubrial process. There is a wider gap between the second 

 and third than between the others. In lionasa, the sternum is narrow and rounded posteriorly 

 in dorso-ventral aspect. In La^opiia. it is square posteriorly and the lateral processes are 

 wider at the tip and shorter than the sternum. These characters are still more pronounced 

 in Centrocercus. 



Pectoral Girdle. The pectoral girdle (figure 77e) is composed of the furcula. coracoids 

 and scapulae. The furcula or wishbone is a forked iione. the head of each meml)pr of which 

 articulates with the head of the coracoid. At its free ventral lip it forms a high thin plate, 

 the caudal border of which is curved gently and not pointed. This plate is low in Lagopus 

 and Tympamtchus. The furcula is V-shaped in Bonasa. but is U-shaped in Centrocercus. 



The coracoid is a stout pneumatic bone, the head of which is hooked medially to form 

 the canal for the tendon on M. supracoracoideus. Laterally, the head is cupped for articula- 

 tion with the head of the humerus. Relow the head, on the dorsn-medial side, is a facet for 

 articulation with the scapula. This is a wide flat facet and is directed obliquely to the length 

 of the bone. Posteriorly the coracoid broadens to articulate with the sternum. On its dorsal 

 surface is a large irregular hole for the entrance of air ducts. The base of the coracoid is tri- 

 angular in outline and, on its medial side, is inserted into the coracoid groove of the sternum. 

 The lateral border is at right angles to the axis of the bodv and lies above the base of the 

 anterior manubrial process. 



The scapula is a thin pneumatic bone extending as far back as the sacrum. In Centrocer- 

 cus, it is straight with a rounded and enlarged tip. It possesses a lateral tubercle below its 

 head which articulates with a corresponding facet on the coracoid. The head forms the medial 

 border of the tendon canal, although it does not completely close it. 



Wing. The wing (figure 77f) has tluec major divisions. The proximal comprises the hu- 

 merus; the medial, the ulna and radius; and the distal, the hand or maiuis. Tlie humerus, 

 the ulna and the manus are all of the same length. 



The humerus is the onlv pneumatic bone in the group. Its proximal end is large and flat- 



