296 THE MUSCLES. 



analogous to those of the pectoraUs magnus, which originate, by their inferioi 

 extremities, from the sides of the sternal keel and the cartilages of the first 

 three or four ribs. They follow the direction of the muscle, and terminate, one 

 above the other, on a short aponeurosis which covers the supra-spinatus, and is 

 confounded with the external aponeurosis of the scapula (Fig. 174, 14). 



Relations. — In its axillary portion, this muscle responds, inwardly, to the 

 lateralis sterni, the first sternal cartilages, and the corresponding intercostal 

 muscles ; outwards, to the pectoralis magnus and transversus. In its prescapular 

 portion, it is in relation, outwardly, with the mastoido-humeralis and trapezius ; 

 inwardly, with the subscapulo-hyoideus, the scalenus, and the angularis of the 

 scapula ; behind, with the supra-spinatus, which is separated from it by the 

 external scapular aponeurosis. 



Action. — This muscle is a congener of the pectoralis magnus, and pulls 

 the scapula backwards and downwards. It is also a tensor of the scap|j|ar 

 aponeurosis. 



DiETERENTIAL ChABAOTERS IN THE MuSCLES OF THE AXILLARY REGION IN THE 



OTHER Animals. 



With regard to the pectoralis anticus and transversus, it is remarked that in the Ox, 

 Sheep, and Pig, the former is small and less distinct from the latter than in Solipeds ; and 

 that in the Dog and Cat, the latter is very thin and narrow. 



In the Ox, the pectoraUs parvus is scarcely distinct from the pectoralis magnus, and 

 which does not extend beyond the inferior extremity of the supra-spinatus. In the Sheep, 

 this muscle is quite confounded with the pectoralis magnus. In the Pig, the pectoralis parvus 

 resembles that of the Horse. Its inferior extremity only covers the first clirondo-sternal 

 articulation ; the superior extremity is more voluminous. With regard to the pectoralis 

 magnus, it terminates on the summit of the external trochanter, after detaching a short branch 

 to the tendon of the coraco-humeralis. The pectoralis parvus of the Dog is very feeble, and 

 terminates with the principal muscle on the humerus. 



Costal Region. 



In each costal region we find fifty-three muscles, which concur, more or less 

 directly, in the respiratory movements. These muscles are : 1. The serrafus 

 magnus. 2. Seventeen external intercostals. 3. Seventeen internal intercostals. 

 4. Seventeen levatores costarum. 5. The triangularis sterni.^ 



Preparation. — 1. Place the subject in the second position. 2. Remove the fore limb and 

 all the muscles attaching it to the trunk, by sawing through tlie scapula as shown in Fig. 

 162, in order to expose the serratus magnus; finish the dissection by taking away all the yellow 

 fibrous tissue which covers its posterior dentations. 3. Study the external intercostals and 

 the levatores costarum, after removing the great oblique muscle of the abdomen, the serrati 

 muscles, the transversalis costarum, and the longissimus dorsi. 4. Excise some external 

 intercostals in order to show the corresponding internal ones. 5. The triangularis sterni is 

 dissected on another portion, wliich is obtained in separating the sternum from the thorax, 

 by sawing through the sternal ribs a little above their inferior extremity. 



1. Sereatus Magnus (Fig. 162, 15). 



Synonyms. — Costo-subacapularis — Grirard. Posterior portion of the serratus magnus of 

 Bourgelat. (A portion of Percivall's serratus magnus.) 



Form — Situation. — A very wide muscle, disposed like a fan, split up into 



' Veterinary anatomists describe in this region a muscle which they designate the costo- 

 gternalis, lateralis sterni, or transveralis costarum, but we consider it a fasciculus detached from 

 the rectus abdominis (see Inferior Abdominal Region). 



