WITH CONE-LIKE PROJECTIONS. 243 



M. 



MALAB. Belonging to the cheek, as the malar bone. 



MALAK PROCESS. Zygomatic process. (Cheek bone process.) 



MASSETER. A muscle situate at the posterior part of the cheek, 

 and lying upon the ramus of the lower jawbone. Its office is 

 to raise the lower jaw and to act in mastication. 



MAS'TODON. An extinct genus of quadrupeds. When alive it 

 must have been twelve or thirteen feet high, and, including 

 the tusks, about twenty-five feet long. The tusks measure 

 ten feet eleven inches, about two and a half feet being im- 

 planted in the socket. According to Owen, the teeth are 

 seven on each side, above and below. The molars have 

 wedge-shaped, transverse ridges, the summits of which are 

 divided by a depression lengthwise with the tooth, and sub- 

 divided into cones, more or less resembling the teats of a cow. 

 In some species there are from three to five ridges to each 

 posterior molar ; in other species five or more. 0. G. Marsh. 

 (The mastodon takes its name from the mastoid or nipple- 

 like processes of its teeth.) 



MASTOID. Having the form of a nipple. 



MAX'ILLARY. Relating or belonging to the jaws. 



MEA'TUS. A passage or canal. 



MEDIAN LINE. A vertical line, supposed to divide a body lon- 

 gitudinally into two equal parts, the one right, the other left. 



MED'TJLLARY. Relating to the marrow, or analogous to marrow. 



MEGATHE'RIUM. An extinct genus of Quaternary mammals. 

 'Megatherium Cuvieri/ from South America, exceeded the 

 rhinoceros in size, its skeleton measuring eighteen feet in 

 length. The vertebra of the tail are very large and power- 

 ful, and that organ, with the hind-legs, seems to have formed 

 a support for the heavy body, while the huge fore-legs were 

 employed in breaking the branches from trees or tearing 

 them down for food. There are four toes in front and two 

 behind. The teeth, five above and four below on each side, 

 resemble those of the sloths. They grew from persistent 

 pulps, and are deeply implanted in the jaws ; they have a 

 grinding surface of triangular ridges, and were fitted for mas- 

 ticating coarse vegetable food. 0. C. Marsh. 



MEMBRANE. A name given to different thin organs, represent- 



