The tibialis anticus. — In the Ruminantia and in the Solipeds, the tibialis anticus is lin planted into the anterior surface of the base of the nietatarsal or cannon bone, so as to be simply an extensor of that portion of the foot which in these animals is usually misnamed the leg.
The tibialis posticus is altogether wanting in the Solipeds, as also in the Ruminantia and the hog-tribe.
The three peronei are, in the horse repre sented by a single muscle, the tendon Of which becomes conjoined with that of the long ex tensor of the digit, with which, when in action, it co-operates.
inserted into the digit. — The ab ductors and adductors* are the abductor pot licis, the adductor obliquus pollicis, the ad ductor transversalis, the abductor mininti digiti, and the interossei.
The flexor muscles in the horse are ne cessarily reduced to a state of extreme sim plicity ; the short flexor communis is entirely wanting ; the plantaris, as described above, considerably increased in importance, has a double insertion into the base of the great pastern bone, and presents a similar disposi tion to that of the flexor perforatus in quadrupeds, while the flexor communis lo'ngus perforans, here reduced to a single tendon, ap propriated to the solitary toe, passes on as usual to be inserted into the last phalanx.
The flexor kngus pollicis exists both in the Ruminantia and Solipeda, notwithstanding the total absence of a thumb in these animals ; but, instead of its usual destination, it here be comes affixed to the tendon of the flexor com munis perforans, to which it forms a powerful auxiliary.
The extensor muscles of the toes in all digitate quadrupeds, provided with a repre sentation of the great toe in the human foot, resemble those of man : in other animals there are some peculiarities that require no tice. In the Quadrumana, the three muscles found in the human foot are present ; but in addition to these there is a proper abductor of the thztmb (adductor, as it would be called by the antbropotomist), situated upon the inner side of the extensor pollicis longus, of which no traces exist in mankind.
Where the inner toe is wanting, as in the dog and the rabbit, the extensor pollicis is likewise deficient.
In the cloven-footed quadrupeds there is a proper extensor to the inner toe representing that of the thumb, and the peroneus longus, which is inserted into the external toe, per forms the office of extending that also : there is moreover in Ruminants a long abductor of the thumb, the tendon of which is inserted close to that of the tibialis anticus In the Solipeds, the extensor conzmunis terminates in a single tendon, which is inserted into the dorsum of the last phalanx of the foot : it receives, however, in transitu, a few fleshy fibres de rived fi.om the cannon bone, which repre sent the extensor brevis of unguiculate quad rupeds.
In the Solipeda, as might be expected, the abductors and adductors of the toes are en tirely wanting.
Muscles which act immediately upon the lower jaw. — These are the nzasseter, the tenzporal, and the two pterygoidei, which in all quadrupeds have the same general arrange ment as in human beings.
Muscles of the The os hyoides of the Solipeds is constnicted in accordance with a plan common to the Ruminants, and many Pachydermatous quadrupeds. Its body is arched and broad, presenting in the middle of its fore part a simple tubercle, and a toler ably long apophysis. It is consolidated with the superior cornua, which together form a very open arch. The single piece forming the anterior cornu is articulated to a rounded tubercle, situated just in front of the union between the posterior cornua and the body of the os hyoides, so as to admit of a consider able degree of motion in this joint. At its termination it is connected to the styloid pro cess, which is very long and slightly forked.
The movements of the os hyoides are ef fected by numerous muscles, derived from several sources, the general arrangement of which, in most quadrupeds, conforms pretty nearly with what occurs in the human spe cies.
The exists in all quadrupeds, or, at least, is represented by a muscle of' cor respondent effect, derived from the sternum. In the Solipeda and in Ruminants, the sterno 113 oideus and the sterno-thyroideus form but a single muscle, which divides, to be inserted into both the larynx and os hyoides.