VIIL] THE MUSCLES. 309 



Palpebral muscles may be wanting, as in Serpents, and the 

 orbicularis palpebraruni may be atrophied, as in \\ hales, or 

 replaced by a complete sphincter, as in Tetraodon. 



The muscles of the nasal region, so important for expres- 

 sion, do not in most animals attain the distinctness they do 

 in man. Yet they may be distinct where little expression is 

 to be detected, e.g, in the Great Ant-eater. They may all 

 abort, as in the Crocodile, or they may receive certain addi- 

 tions, as in the Pig, where two muscles arise, one on each 

 side, from the zygoma and maxillary bone, and unite together 

 above the end of the snout, which they elevate ; while two 

 other muscles (which depress the snout) take origin, one on 

 each side, from the zygoma, and are inserted into the median 

 septum. In the Mole there are even four on each side, all 

 arising above the ear and passing forwards between the tem- 

 poral and masseter muscles, to be inserted into the extremity 

 of the muzzle. 



The most exceptional modification of the nasal and labial 

 muscles is, however, found to exist in the Elephant, where 

 they form its remarkable trunk. For this purpose two 

 muscles (elevators) take origin, one on each side, from pro- 

 cesses above the nasals. Another pair (depressors) spring 

 from the pre-maxillas, while a third pair (lateral, longitudinal 

 muscles) take their origin from the frontal and maxillary bone 

 on each side. Besides these there are intrinsic muscles of 

 the proboscis, the fibres of which radiate from the nasal pas- 

 sages to the inner surface of the skin, and tend to keep 

 the former open. 



Another peculiar condition is that existing in Cetacea, which 

 will be noticed in treating of the nose as a sense organ. 

 Here, however, it may be mentioned that in the Porpoise a 

 muscular layer spreads forwards from the frontal bone over 

 the posterior nasal structures, and another layer spreads back- 

 wards from the maxillary bone over the anterior nasal struc- 

 tures. It is by the contraction of these muscles that the nasal 

 passage is opened while the nasal sacs are compressed and 

 their contents ejected. 



The masseter may attain a relative size and complexity 

 which are very much greater (especially when compared with 

 the simultaneous condition of the temporal) than in man. 

 This great development is well seen in certain Rodents, e.g. 

 Lagostonms and the Agouti, where the masseter is divided 

 into three portions, and traverses the singularly enlarged 

 infra-orbital foramen spoken of in describing the skeleton. 



