MR. MAYHEW ON PHYSIOLOGY OF THE HEART. 265 
branes,” although they act in some mysterious way “ to keep 
the blood left within the aorta, or pulmonary artery, from 
mingling with the fluid poured into the ventricles.” 
Mr. Mayhew states, in the first place, that although tf< it is 
very general to say, that arteries have three coats, one of 
which is muscular,” yet he has “ in vain endeavoured to dis- 
cover anything approaching to organic fibre in the tubes of 
arteries.” Now, although it was at one time thought that 
the middle coat of arteries was entirely composed of yellow 
elastic fibrous tissue, it has been clearly shown by many 
eminent microscopists, especially by Professor Kolliker, and 
can easily be demonstrated, that in this coat many organic 
muscular fibres are to be found ; in fact, that in some arteries 
they form the greater part of the middle coat. ce However,” 
as Mr. Mayhew T very justly remarks, u the blindness of one 
man makes no way when urged against the positive percep- 
tions of another.” Again, had Mr. Mayhew been keeping up 
with the knowledge of the day, he might have known that 
the middle coat of veins, like that of arteries, is partially 
muscular, and has been recognised as muscular for years. 
Mr. Mayhew may have been taught that the venous coats 
are not muscular ; but it is surely the duty of every profes- 
sional man, before he writes for the instruction of his brethren, 
to make himself aware of all the previously ascertained facts, 
with regard to the subject of which he treats. 
Mr. Mayhew says that he has been unable c< to investigate 
the smaller vessels by means of the microscope,” and yet 
presumes to doubt the existence in their walls of organic 
muscular fibre-cells, of such minuteness, that two thousand 
of them would lie on an inch. What other instrument but 
the microscope could be used for the detection of these objects? 
After this digression, which, for his own credit, might have 
been omitted, Mr. Mayhew goes on to say that, according to 
the present theory, the blood is propelled from the auricles 
to the ventricles by the contraction of the former. To this 
he takes objection, from the fact of the circulation being 
carried on in a heart with an ossified auricle, which could 
contract very slightly, if at all. So far, so good. But he 
remarks, with the air of one who has made a great discovery, 
that the venae cavae and pulmonary veins possess a distinct 
muscular covering, and that their contraction assists that of 
the auricles to fill the ventricles. This is no new discovery. 
The muscular covering of the cavae of the horse extends on 
the anterior cava to the axillary vein, and on the posterior 
cava to the diaphragm. This coating, however, appears to 
be stronger on the pulmonary veins than on the cavae. These 
