MOUTH OF MAMMALS. 391 



are disposed in a straight line from side to side ; external and 

 posterior to these again the muscular fibres resume the radiated 

 course. The second series of muscles tend to diminish, but can- 

 not close, the areaB of the nasal passages ; the first and third series 

 contract the diameter of the trunk without affecting that of the 

 canals. All the muscles are distinct, and terminate at both ex- 

 tremities in slender tendons : they are imbedded in a cellular 

 texture occupied by a white homogeneous substance. 



The other muscles of the proboscis are disposed longitudinally, 

 in a multitude of fasciculi, dispersed in short curves, so that the 

 two extremities of each fasciculus are implanted into the mem- 

 branous tubes, while the convexity of the arch is adherent to the 

 external aponeurosis. These fascieuli surround the whole trunk, 

 throughout its length ; their eifect being to shorten it from end 

 to end or in any part, and by partial contractions, on one side or 

 the other, to bend the trunk in any direction. The longitudinal 

 fasciculi are derivations from four great muscles, which, though 

 almost blended together in the trunk itself, have distinct origins. 

 Of these the two anterior arise from the whole breadth of the 

 frontal bone above the ossa nasi, while the two lateral muscles 

 take their origins from the superior maxillary bones beneath and 

 in front of the orbit, answering to those in the Tapir, fig. 155, a. 

 The posterior surface of the basal part of the proboscis is supplied 

 with fibres which seem to be continuations of a muscle answering 

 to the orbicularis oris of the Tapir, ib. d, d, and. which run 

 obliquely downward and inward so as to meet their fellows from 

 the opposite side at an acute angle. With such a structure it is 

 evident that the nasal prolongation of the proboscidian Pachy- 

 derms is able to move in every needful direction, and perform all 

 the duties of a lithe and flexible arm. 



In the Horse, the callous roof of the mouth is disposed into 

 about sixteen curved ridges, with their convexities forward. 

 Many mucous crypts perforate the membrane, above which, as in 

 other Ungulates, is a remarkable plexus of veins and nerves. The 

 pharynx is capacious and communicates w r ith the pair of large sac- 

 culi at the ends of the eustachian tubes. The muscle which repre- 

 sents the middle constrictor descends from the pterygoid and palate 

 bones, along the sides of the pharynx, around which the fibres wind 

 obliquely, uniting in the middle line upon its posterior surface, 

 where they form a thick muscular layer. The inferior constrictor 

 is equally broad and strong, its fleshy fibres taking nearly the 

 same direction as they proceed towards the back of the pharynx, 

 where they join by a median raphe. In addition to the above, 



