MUSCLES OF THE TRUNK. 299 



Differential Characters in the Muscles of the Costal Region in the other 

 Animals. 



The muscles of the costal region caunot be tlie same ia number in all the domesticated 

 animals ; the intercostals and levatores costarum, for instance, must vary in number with that 

 of the ribs. Beyond this, the differem^es are slight. In the Ox, the serratus magnus is very 

 extensive, and the portion which passes to the posterior triangular surface of the scapula is 

 readily distinguished from the anterior by its diminished thickness, the larger proportion of 

 aponeurotic iibres it contains, and the flattened tendon by means of which it is inserted. In 

 the Pig, it is remarked that the internal intercostals are prolonged— maintaining a certain 

 thickness — to near the vertebral spine. 



Comparison of the Thoracic Muscles of Man with those of the Domesticated 

 Animals. 



The muscles of the axillary and costal regions and the diaphragm, are named the thoracic 

 muscles in Man. 



The pectoral muscles are distinguished into great and small. The pectoralis magnus corre- 

 sponds to the pectoralis anticus and trausversus of the Horse. It is attached, on one side, to 

 the inner two-thirds of the clavicle, the anterior face of the sternum, and the cartilages of the 

 first six ribs ; on the other, to the anterior border of the bicipital groove, and, by a fibrous 

 expansion, to the aponeurosis of the arm. The costal fasciculi are distinctly separated from 

 the clavicular atid sternal fasciculi 



The small pectoral, which corresponds to tlie pectoralis magnus and parvus, is inserted, on 

 the one part, into the external face of the third, fourth, and fifth ribs ; on the other part, by a 

 tendon to the anterior border of the coracoid process. 



In Man, there is found a muscle whicli does not exist in animals; this is the subdavius, a 

 very slender fasciculus situated beneath the clavicle, and attached to the cartilage of the first 

 rib and the external portion of the lower face of the clavicle (see Fig 164, 5). 



The serratus magnus does not show any distinct aponeurosis on its surface ; it arises from 

 the eight first ribs, and its digitations are grouped into three princip;d fasciculi. 



Lastly, in Man the internal intercostals are prolonged to the vertebral column by small 

 muscles, named intra-costals. • 



INFERIOR ABDOMINAL REGION. 



The lateral and inferior walls of the abdominal cavity are formed by a wide 

 musculo-aponeurotic envelope, which rests, by its periphery, on the sternum, 

 ribs, lumbar vertebrae, ilium, lumbo-iliac aponeurosis, and the pubis. This 

 envelope is concave on its superior surface, and results from the assemblage of 

 four pairs of large membraneous muscles aiTanged in superposed layers. Reckon- 

 ing them from without inwards, these are designated the (/reat, or external oblique, 

 the small, or internal oblique, the great straight, and the transverse muscle. 

 Covered outwardly by an expansion of yellow fibrous tissue — the tunica abdomi- 

 nalis — and separated from those of the opposite side by the linea alba — a medium 

 raphe extending from the sternum to the pubis — these muscles support the 

 intestinal mass, and by their relaxation or contraction adapt themselves to the 

 variations in volume which these viscera may experience. 



Preparation.—Miex placing the animal in the first position, a wide opening is to be made 

 in the pectoral cavity by the ablation of a certain number of ribs, which should be divided 

 inferiorly, above the costal attachments of the great oblique muscle. The heart and lungs are 

 removed; then an incision is made in the diaphragm, to allow the digestive viscera contained 

 in the abdominal cavity to be taken away. It is not absolutely necessary, however, to empty 

 that cavity, and if its contents be allowed to remain, several punctures should be made in the 

 large intestine to prevent the accumulation of gas, and the too great distension of the abdominal 

 parietes. 



These preliminary precautions having been adopted, then proceed in the following 

 manner : — 



