780 MAMMALIA. 



to each of the fingers that correspond to the four outer fingers of the 

 human hand, whilst in Man the index and little fingers only have 

 auxiliary extensors. 



(2244.) The abductor and extensor muscles of the thumb are not so 

 perfectly developed in any animals as they are in the human hand. The 

 short extensor, in fact, is wanting even in Monkeys ; and in the lower 

 orders of quadrupeds even the extensor longus and abductor are blended 

 together, or totally wanting. 



(2245.) The deep and superficial flexors of the fingers are very gene- 

 rally met with, the number of tendons furnished by each corresponding 

 of course to that of the fingers themselves ; but in the Solipeds the two 

 muscles are almost blended together. Even in the Ruminants, although 

 these muscles remain separate, their tendons become confounded toge- 

 ther, and divide again, to be inserted into the phalanges to which they are 

 appropriated. In these Ungulata, too, as we need scarcely say, the lum- 

 bricales and interossei are quite deficient ; and the short muscles of the 

 thumb are completely developed only in Man and in the Quadrumana. 



(2246.) It is in the human species only that the lower extremities are 

 organized so as to maintain the body in the erect position ; and in con- 

 sequence, the glutcei muscles in the human body are enormously deve- 

 loped when compared with those of the lower animals ; but the other 

 muscles derived from the pelvis and thigh present but slight differences 

 throughout the whole class under consideration. In the leg and foot 

 likewise it is not difficult to identify the muscles that correspond to 

 those found in the human subject, but, as in the anterior extremity, 

 modified in their disposition and mode of insertion in accordance with 

 the construction of the skeleton. 



(2247.) The articulations whereby the different pieces composing the 

 Mammiferous skeleton are connected to each other are constructed upon 

 the same principles as in the human body, insomuch that to describe 

 them even in general terms would be useless. 



(2248.) The bones of the cranium and face, as in Man, are joined 

 together by harmony or by suture. The articulations of the lower jaw 

 are double, each presenting an interarticular cartilage, except in the 

 Cetacea, where, instead of such a structure, a very thick, matted, liga- 

 mentous substance, having its interstices filled with oil, passes directly 

 from the condyles of the jaw to the temporal bones. 



(2249.) The joints of the spine, thorax, and pelvis are all constructed 

 upon the same principles as the corresponding articulations in the human 

 subject ; and the same may, with slight exceptions, be said of those of 

 the extremities. The chief differences will be found in the connexion 

 between the radius and ulna, the movements of rotation becoming gra- 

 dually less manifest as we descend from Man : the tibia and fibula, too, 

 ultimately become completely anchylosed to each other. The hip-joint 

 contains an internal liyamentum teres -, but in a few instances, e. g. the 



