174 MUSCULAR SYSTEM. 



breadth, and by sending its fibres both forwards and back-- 

 wards from the depressed zygomatic arch, it assists in the 

 longitudinal movement of the lower jaw in both these direc- 

 tions. The whiteness, or pale colour, and the velocity of 

 movement of the muscles of rodent quadrupeds, present 

 further affinities to the class of birds, especially to the heavy 

 inactive vegetable-eating gallinaceous kinds, where the blood 

 is less rapidly and less extensively distributed through their 

 muscular system than in the more powerful rapaceous tribes. 

 The flexor muscles of the arms are generally much deve- 

 loped and much exerted in this order of quadrupeds, either 

 for scraping the ground for food, or for burrowing in the 

 earth, or for climbing upon trees and cliffs. In the 

 marsupial quadrupeds, the abdominal pouch is em- 

 braced externally by the panniculus carnosus, the fibres of 

 which serve, by their extension over the pouch to the sym- 

 phisis pubis, to contract that cavity so as closely to embrace 

 the newly-received young, and to protect them during the 

 first period of their extra-uterine life. Within this pouch 

 are the mammary glands, which are embraced by distinct 

 muscular fasciculi destined to compress them and to aid the 

 escape of their secretion, and other delicate fasciculi force 

 the milk from the ducts and the nipples into the mouth of 

 these abortive foetuses, and thus to extend the nipples from 

 their ordinary retracted condition. The muscular system 

 of carnivorous quadrupeds corresponds, in its high develop- 

 ment with the solid texture of their bones, and the great 

 extent of their respiration, the nutritious character of their 

 food, and the living habits and wants of the species. By 

 the magnitude and the extension forwards of the zygomatic 

 arch their large temporal and masseter muscles have an ad- 

 vanced insertion on the lower jaw, most favourable to their 

 action, which is aided by the short truncated or rounded 

 form of the head, especially in the feline animals. The leva- 

 tor muscles of the lips and nose serve, by their magnitude, 

 to uncover the large tusks, to prevent injury of the lips in 

 seizing the prey, and to add ferocity to the aspect to in- 

 timidate and overcome that prey. The muscles of their short 

 and thick neck are strong, to enable them to carry off their 

 prey entire, or to tear it to pieces, as those of their shoulder 

 and arm are powerful, to enable them to grasp or hold down 



