The sacro-lumbalis prises, in conjunction with the latissimus dorsi, from the back of the sacrum, and also by flat tendons about half the breadth of the muscle from the superior edge of all the ribs, except two or three of the most anterior ; and its slips are in se ted by as many distinct tendons into the inferior edge of all the ribs, except two or three of the hindmost, and also into the trans verse process of the seventh vertebra of the neck. The continuation of this muscle, the cervicalis descendens, ofrers nothing remarkable.
The multifidus spince,. in the dorsal region arises by numerous tendinous origins from the transverse processes of the vertebrm of the back, loins, and sacrum, near their pos terior protuberances, each slip running for wards to be inserted into the spinous pro cess of the vertebra in front of that from which it derives its origin, the whole forming a thick mass, which fills up the hollow situated between the spinous and transverse processes. In the neck a similar disposition exists.
The interkansversarii colli take their origins from the roots of the oblique processes of the cervical vertebrm, and from between these and the transverse processes : in the horse they are of great strength and importance, running forwards to be inserted into the trans verse processes of the vertebra in front of that from which they arise. In addition tou the above there is a set of' muscles named by Stubbs the intervertebraks, which do not exist in the hu man subject : these arise from the ascending oblique processes of the five inferior vertebrm of the neck, and from the space betwixt the oblique processes of the uppermost vertebrm of the back : they are each of them inserted into the lateral parts of the bodies of the ver tebrm above their origin.
The longus colli is the only muscle, ex clusively appropriated to the movements of the spine, situated in front of the spinal column. This muscle, in the horse, arises from the transverse processes of the third, fourth, fifth, and sixth vertebrm of the neck, from which origins it runs upwards to be in serted by distinct tendons into the anterior part of the bodies and transverse processes of the vertebrw above them, and into the anterior surface of the atlas.
The quadratus lumborum offers the same disposition as in the human subject.
The tail in quadrupeds, from its great de velopment,requires for its movements a special set of muscles, of which scarcely any traces exist in the human subject. This organ in the horse is susceptible of three kinds of movements. It can be straightened or ele vated, bent or brought downwards, and lastly carried to either side. These movements, again, by their combinations, produce secon dary effects, so that the tail becomes suscep tible of very extensive motions ; and, in such quadrupeds as have this part very largely de veloped, it even supplies the place of a hand, so completely is it under muscular control.
In order to effect these different movements, three* distinct sets of muscles are employed, which are arranged upon the same plan as the long muscles in other parts of the spinal column ; that is to say, they arise by numerous tendinous slips, and are inserted in a similar manner, the slips of origin and insertion run ning, of course, in opposite directions : the latter, moreover, are prolonged to a much greater extent than in the rest of the spinal column, and firmly bound down to the ver tebrm by tendinous sheaths, so as to add as little as possible to the bulk of the tail.
The muscles which raise or straighten the tail are all situated upon its upper aspect : they are, first, The superior caudien). This muscle arises in the horse from the inferior or posterior edge of the third spinal process of the os sacrum, and from the spines, edges, and interspinal ligaments of the sacral vertebrw behind that point, as well as from those caudal vertebrm that are pos sessed of spinous apophyses. The fleshy mass formed from these origins gives off numerous slender tendons : the first of these is the shortest, and runs inwards to be in serted into the base of the first caudal ver tebra, in which the articular apophyses are wanting. The second tendon is inserted in a similar manner into the succeeding vertebral piece; the third into the next, and so on to the end of the tail. The nuinber of the tendons given off is, of course, determined by that of the vertebrw. Each tendon is lodged in a sort of ligamentous canal, which forms a sheath for it throughout its whole course. When these two muscles act in concert the tail is necessarily raised upwards.