10 
Mr. Carlisle’s Lecture on the Arrangement 
the hook ; but the same effects take place when the hook is 
fastened to the side, or tail. This prostration of strength may 
depend partly on fear, and partly on interrupted respiration, 
since fishes, when swimming rapidly, keep the membranes 
branchiostegce closed, and when nearly exhausted, act violently 
With their gills. 
The shortness of the muscular fibres, and the multiplied 
ramifications of the blood-vessels, are probably peculiar 
adaptations for the purpose of gaining velocity of action, 
whrbh seems to be invariably connected with a very limited 
duration of it. Such examples form an obvious contrast with 
the muscular structure of slow-moving animals, and with 
those partial arrangements where unusual continuance of 
action is concomitant. 
Since my former communications on the subject of cylin- 
drical arteries,* another instance of their supplying slow- 
moving muscles, which are capable of long continued action, 
has been pointed out to me by Mr. Macartney. It is in the 
muscles, which act upon the feet and toes of many birds, and 
seems to be an adaptation for the long exertion of those 
muscles while they sleep, and also when they alternately 
retract one foot under the feathers to preserve it from the 
effects of cold. 
The muscles of the human body, which perform the most 
sudden actions, have their masses of fibres subdivided by 
transverse tendons, or are arranged in a penniform direction. 
The semi-tendinosus, and semi-membranosus of the thigh are 
thus constructed ; the former having its fleshy belly divided 
by a narrow fascia, and the fibres of the latter being ranged 
f Phil. Trans. 1800, p. 98. — .Also 1804, p. 17. 
