TRANSACTIONS OF THE SECTIONS. - 189 
the almost simply diffused muscular masses of fishes and those of mammalia, so 
variously complicated in appearance, through intermediate terms safely appreciated, 
With these presumptions for a guide, and using the necessary impartiality in viewing 
facts, and patience suited to the intricacies which this system so often presents, the 
investigations have been pursued, and the results already obtained appear both satis- 
factory and promising. Such of them as would appear sufficient to indicate a thread 
of connexions between the two extremes in the disposition of muscles in vertebrata, 
and afford a general view of it, were intended for communication to the Section, and 
could be briefly summed up in the following statements. 
A repetition of parallel membranes stretched between skin and skeleton, and cor- 
responding in number with the segments of the latter, are met with in fishes and lower 
reptiles, where muscular portions, which fill their intervals with fibres parallel to the 
axis of the body, are called myocomata. The membranes descend from the back to 
the abdomen in waving or zigzag ribbons, having their concave and conyex surfaces 
alternately turned forwards and backwards. The character of ribbons becomes soon 
lost by the membranes being found to protrude alternately on one side, and forwards 
or backwards according to the convexities of the angles; thus pouches being formed 
more or less long and funnel-shaped, The pouches, which are insinuated in one 
another, are met with gradually elongating, so as to stretch over several vertebra, 
and in proportion as they do so, they become more and more obliterated at the bottom, 
which is effected through accretion of the side walls to a lamina, this lamina being 
then found to extend gradually as a crest on the upper wall of the pouch, In the 
pean the whole pouch has become a lamina, receiving the muscular fibres on its - 
anks. 
_ Before proceeding further, the divisions of the lateral masses of fishes in longitudinal 
direction must be taken notice of. Some fishes present no division on the mesial line 
of the side; others do, having thus a dorsal and an abdominal portion separated ; in 
others the portions or longitudinal stripes are three, four, &c., according to the 
species. The number of the stripes does not correspond to that of the angles; but the 
distinction not only exists virtually, as it appears from real divisions in other fishes, 
but also if an angle be not comprehended between two divisions, another angle is 
formed, The greatest number of angles or series of pouches with real longitudinal 
separation from one another met with, is exhibited by gymmetrus, the amount being to 
above thirty-five. Thus the myocomata are divided in several collateral elements, 
recombining in their longitudinal succession to collateral series; and in proportion as 
the longitudinal series become independent, the myocomatical character of the masses 
disappears. These elements being anatomically so well defined and of great im- 
portance in the operations of nature to attain a higher development of the muscular 
masses, a term becomes necessary to designate them, as well as the longitudinal 
series; for the element, the term myisk has been proposed and made use of, and for 
a longitudinal series of myisks, that of myostichia. If several myisks of higher ani- 
mals be ascertained to belong to one transverse set, the myocomata of fishes would 
evidently reappear. 
We must now come back to the Skates, Their myisks begin from the bottom of a 
myostichial channel, and accosting the walls of the latter, they ascend to the surface 
of the myostichia, to be prolongated in a membranous expansion, bearing a mesial 
tendon, the prolongation of the lamina. The myisks of the Skate, as well as their 
tendons, being superposed upon one another, it has been made probable that this is 
effected by the lower walls of the pouches accreting to the bottom of the channel. 
The myisks stretchiug over several vertebree, every corresponding segment of the 
channel will appear sending off fasciculi to several of them. In serpents and lizards, 
the fasciculi coming from one segment for the first time, appear depending on tendons, 
at first on one side only, then on both. ‘The next step is found in myostichias of the 
same animals, and consists in the modification, that only one side of the channel gives 
off fibres to the myisks, while on the other side the corresponding walls of the pouches 
present mere membranes more or less blended with the channel wall, and help to con- 
stitute the vagina for the myostichia and its tendons. Birds and mammalia present 
ho more essential modifications of the myisk, and the differences are reduced to 
atrophic, or aponeurotic appearance of the mentioned fascias or prolongation of the 
pouches. -An illustration for the mammalia has been made on the sacro-lumbalis. of 
the rabbit. The origins of the muscle from the ribs would correspond to the several 
