671 
LECTURES ON HORSES. 
By William Percivall, M.R.C.S., Veterinary Surgeon to the 
First Life Guards. 
MUSCULAR MOTION. 
The property possessed by an animal body of locomotion or self- 
movement is of a nature altogether different from any we witness 
in machinery: how ingenious soever a piece of mechanism may be, 
and imitative of the movements of the vital machine, there is still 
this essential difference between them — that one moves through an 
extrinsic force or power communicated to it; whereas, in the other, 
the power of motion is created or generated. It is, in the strictest 
sense of the words, a self-moving machine, the other being but 
self-moved : and in the muscles reside the source of motion. 
They, during life, possess power of contracting or shortening 
their lengths, through which simple change all the movements 
of the body are brought about. What it is that enables them to 
contract, what alterations of structure or arrangement they undergo 
during contraction, is a question that has puzzled those who have 
made themselves best acquainted with their intimate texture and 
organization. We must, therefore, content ourselves with a know- 
ledge of the established facts, that the self-moving power resides 
in the muscles, and is dependent on their vitality ; dead muscle, 
or flesh, being devoid of any such property. 
The contraction of a muscle has the effect of bringing nearer 
together the parts to which its ends or extremities are attached ; 
either both attachments move in approximation, or, one being fixed, 
the other moves towards it. The tail, e. g. (which is a good ex- 
emplification of muscular action), is raised by the contraction of 
muscles running from the croup to its upper surface, called, from 
their office, the erector es coccygis ; and is depressed by muscles 
running underneath, from within the pelvis to its under surface, 
named the depressores coccygis. There are likewise two other 
muscles, one on each side, having the power of curving or flexing 
the tail around the quarter, either to the right or left side, accord- 
ing as the right or left muscle is in action. Altogether there are 
eight — four pairs of — muscles belonging to the tail : two for rais- 
ing it, two for depressing it, two for forcibly compressing it against 
the rump, and two for curving it either on one side or the other. 
Less than eight muscles would have proved insufficient for the 
