302 3fuscles of the Chelonian Shoulder-girdle. 



extends upward and forward, called the coracoid process (PI. 12, fig. 1, 

 c). The axillary border of the scapula (PI. 12, fig. 1, b.) is thickened, 

 and is connected with the " spine " by a thin sheet of bone. The 

 " acromion process " is articulated with the clavicle wliich passes 

 from it to the sternum. The clavicle is also attached to the " cor- 

 acoid process " by a ligament. 



The shoulder-girdle of the Chelonian (PI. 13, figs. 1 and 2) is com- 

 posed of three shafts of bone, diverging from the glenoid cavity. One 

 (PI. 13, fig. 1, b'.) is attached proximally to the under side of the ante- 

 rior part of the carapace by a ligament near to the first dorsal verte- 

 bra. The other two lie in a hoi-izontal position, the one (PI. 1 3, fig. 



1, a'.) running from the articular end of the girdle to the anterior ]tart 

 of the upper side of the plastron, and attached to the latter by a 

 strong ligament at its medial line ; the third part runs oblicpiely 

 toward the center of the plastron, its proximal or medial end being- 

 more or less free. 



In homologizing the elements of these shoulder-girdles, the follow- 

 ing results have been reached. The perpendicular shaft (PI. 13, figs. 1, 



2, b'.) of the Chelonian is regarded as the representative of the "exter- 

 nal "" or "axillary" border of the human scapida (PI. 12, fig. 1,1).), 

 and may be called the scapida proper. 



The second anterior horizontal shaft of the girdle (PI. 13, figs. 1, 5, 6, 

 a'.) represents the "spine" and "acromion process" together, of the 

 human scapula (PI. 12, fig, 1, a. s.), and may be called the acromion. 



The third, or posterior horizontal element (PI. 13, fig. 1, c), repre- 

 sents the " coracoid process," and may l)e called the coracoid. 



F'rom the "posterior" surfiice of the human scapula and its pro- 

 cesses arise six or seven distinct muscles. Let us consider them sep- 

 arately, in their relations of origin and insertion. 



The " teres major " arises from near the medial end of the axillary 

 border of the scapula (PI. 12, fig. 1, i): part of the "latissimus dorsi" 

 sometimes arises from the extreme end of this border (PI. 12, fig. 1,2): 

 the direction of these two muscles, as well as their action and areas 

 of insertion on the humerus, are closely related. The corresponding 

 muscle in the Chelonians (PI. 13, fig. 1, 1), called " teres major" by most 

 all writers on the subject, arises from the anterior face of the scapida., 

 the area of origin being a narrow line extending from the medial end 

 to the acromio-scapular angle. It is inserted into the neck of the hume- 

 rus together with the representative of the " latissimus " (PI. 1 3, fig. V, 1). 



There is considerable difference in the positions of the areas of 

 insei'tion of this muscle, here and in man, the discussion of which 

 will not be introduced at this place. 



