MUSCLES OF TUE TRUNK. 299 



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



Animals. 



The muscles of the costal region cannot be tlie siiiue in number in all the domesticated 

 animals ; tlie intercostals and levatorcs costarum, for instance, must vary in number with that 

 of the ribs. Beyond thL-j, the differences are slight. In the Ox, tlie serratus niayuus is very 

 exti-nsive, and tiie portion which passes to the posterior triangular surface of tlie scapula ia 

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

 a[)oneinotic tibrcs it contains, and tlie fiattem-d tendon by means of which it is inserted. In 

 the Pig, it is rcmarived tlmt the internal intercostals are prolunged — 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 

 mtiscles in ^lan. 



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

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

 the inner two-thirda 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 bici[iital groove, and, by a fibrous 

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

 the clavicular and sternal fasciculi 



The small ptctoral, which corresponds to the 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 tiie coracoid process. 



In Man, there is found a muscle which does not exist in animals; this is the suhdavius, 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 principal fasciculi. 



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

 muscles, named inlra-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 vertebrie, ilium, lumbo-iliac aponeurosis, and the pubis. This 

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

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

 ing them from without inwards, these are designated the ^rpuf, or external oblique, 

 the small, or infernal ohlique, the great straight, and the transverse muscle. 

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

 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. — After 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 

 interiorly, above tlie 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 precautious having been adopted, then proceed in the following 

 manner : — 



