M. ENTOPECTORALI8. 241 



654. Origin. By fleshy fibers, from the lateral border of the 

 pr ester nal keel, and from the first mesosterneber and part of the 

 second, thus filling the interval between the origin of the cephalic 

 division and that of the pecto-antebrachialis, do. caudalis. 



Insertion. Along a line occupying, approximately, the second 

 and third fifths of the ventral border of the humerus, thus ventrad 

 of the lines of insertion of the cephalic division, and of the ectal 

 lamina. The insertion is somewhat variable in detail, but a simple 

 form is the following: The cephalic half continues fleshy to the 

 bone, while the caudal half is inserted by a thin tendon 3-7 mm. 

 long. The proximal end of the line of insertion is nearly opposite, 

 but 2-3 mm. ventrad of, the distal end of the line of insertion of the 

 cephalic division, and the distal end is close to the distal end of the 

 line of insertion of the ectal lamina. 



M. ENTOPECTORALIS. 



655. Remark. The remainder of the pectoral mass forms at least three divisions 

 which are sufficiently distinct in origin or insertion to warrant separate descriptions, but 

 which, perhaps, are all parts of what may be regarded as a large representative of the 

 "pectoralis minor" of man ( 572). 



Thes3 muscular divisions are very variable in number, form, connection with each other 

 and osseous attachment. In respect to size there are marked differences between individ- 

 uals ; in young or feeble cats, the masses may be not only thin, but more or less subdivided, 

 while in adult or robust animals, they are sometimes almost continuous with each other. 



Exposure. So much as was not concealed by the M. ectopecto- 

 ralis is covered by a dense layer of connective tissue which must 

 be removed. 



DV. CAUDALIS. 



656. Synonymy. "Le premier chef du grand pectoral," S.-D., A, II, 341 ; pectoralis, 

 part 3 (in part), Miv., B, 147. 



Figures. The ectal aspect (72, both sides); humeral end, reflected (73); insertion 

 line (69, 70). 



General Description. A thick band, from the 6th mesosterne- 

 ber and sometimes the xipJiisternum to the proximal half or two 

 fifths of the ventral border of the humeral diaphysis. 



Dissection. The line of separation between the cephalic and, 

 caudal divisions is about midway of the width of the whole mass, 

 at about 3 cm. from the humerus ; it coincides nearly with a line 

 drawn from the surgical neck of the bone in the direction of the 

 fibers of the muscle. The degree of separation varies greatly, and 

 16 



