PECTOBALIS GROUP. 23o 



Triceps (§§ 687-680).— The caudal or eotal aspect of tlie entotriceps appears on both ■ 

 sides, but the divisions are not defined. 



Xiphi-humeralu (§ 660).— On the right the sternal part is shown but not named. On 

 the left, its course entad of the eniopectoralis is indicated by the broken lines, and part of 

 its humeral end is seen. Usually this muscle is more intimately connected with the 

 xiphisternum. 



PECTOEALIS QEOUP. 



§ 640. General Remark.— The two pectoral muscles of man, 

 ectopectoralis, "pectoralis major," and eniopectoralis, "pectoralis 

 minor," are represented in tlie cat by several muscles to which 

 Straus-Durckheim and others have applied distinct names. Most 

 of these divisions, however, may be recognized as parts of two 

 masses, an ecfal or superficial, arising nearer the cephalic end of 

 the sternum, and extending laterad to the diaphysis of the hume- 

 rus, and an ental or deep, arising from the caudal part of the ster- 

 num, and extending later o-ceplialad to the liead of the bone. The 

 former, representing the ectopectoralis, tends to subdivide into 

 superposed laminae; the latter, representing the entopectoralis, 

 tends rather toward a division into parallel fasciculi. See § 572, 

 Humphrey, E, 110, and Wilder, 30, 306. 



§ 641. Crossing of the Pectoral ^Zemerai«.— Excluding the M. pecto-antebrachialis, 

 which is inserted upon the antebrachium, the pectoral mass may be roughly described as 

 a series of four superposed laminae crossing one another in such a way that the cephalic in 

 origin, is distal in iiisertion, while the caudal in origin is proximal in insertion. 



The octal lamina of the M. ectopectoralis (Fig. 72) arises from the prassternum and ceph- 

 alad of it, and is inserted upon the middle third of the humerus. The ental lamina, as a 

 whole, arises from the cephalic third of the sternum, and is inserted upon the proximal 

 three fifths. The M. entopectoralis, as a whole, arises from the entire mesostemum, and is 

 inserted upon the proximal third. Finally, the M. xiphi-Mimeralis arises from or near the 

 xiphisternum, and is inserted upon the head and neck of the humerus. 



It follows from this arrangement that the general direction of the fibers of the first por- 

 tion is nearly transverse ; that, in the natural attitude of the arm, for a part of their course 

 at least, the fibers of the last portion run nearly parallel with the meson ; while the direc- 

 tions of the other two portions are intermediate. 



A somewhat similar relation exists between the less distinctly separable regions of the 

 human ectopectoralis as described by Gray (A, 400) and Quain (A, I, 193). 



The insertion lines of the two laminse of the ectopectoralis are nearly parallel, but 

 almost meet at their distal ends (Pig. 69). If they were continuous, they might be de- 

 scribed as a single line folded upon itself, and their tendons would be strictly comparable 

 with the tendon of the human pectoralis major as described by Gray and Quain. 



§ 642. I7ie Pectoral Complexity. — In the cat there may be recognized eight or nine 

 elements of the pectoral mass, more or less independent as to origin or insertion or both. 

 In man, the M. entopectoralis (P. minor) is distinct, and the M. ectopectoralis is more or 

 less readily in different subjects separable into two or three portions, whose origins and 

 insertions, however, are nearly or quite continuous. 



It may be said, therefore, that the provision for separate and independent movement 



