122 PHILOSOPHY OF ZOOLOGY. 
of phosphate of lime. They are either connected with the 
digestive system, as the teeth in the stomach of the lobster, 
or the jaws and teeth of the Sea-Urchin, (Echinus,) or they 
constitute a central support for the soft parts, as the bone 
of the Cuttle-fish, or the stalk of the Sea-pen. 
CHAP. VIII. 
ON THE MUSCULAR SYSTEM. 
Havine considered, in the two preceding chapters, the 
integuments which invest, and the bones which support, the 
animal frame, we are now prepared to consider the organs 
by which motion is executed, constituting the muscular sys- 
tem. 
The investigation of this class of organs, unfolds the 
most singular mechanism of parts, and an infinite variety 
of movements, enabling the animal to perform the internal 
and external actions necessary to its existence. 
The muscles appear in the form of large bundles, con- 
sisting of cords. These, again, are formed of smaller 
threads, which are capable of division into the primary fila- 
ments. Each muscle, and all its component cords and fila- 
ments are enveloped by a covering of cellular membrane, 
liberally supplied by bloodvessels and nerves. 
The primary filaments appear to be parallel, and to be 
of very small demensions. Procuaska* found them 
at only 355, or the size of the globules of the blood, 
when deprived of their colouring matter +. Differences of 

* «Tn meis experimentis maxima globula rubri sanguinis diameter com- 
parata cum diametro fili carnei se habere videbatur ut 8 vel 7 ad 1; unde 
concluditur filum carneum a globulo rubro sanguinis superari crassitie sua 
vicibus inter quadraginta et sexaginta.”’—Operum Minorum, pars 1. p. 198. 
+ Phil, Trans. 1818, p. 175. 
