OF THE MUSCULAR STRUCTURE. 75 



Of the Formation and development of the Muscular Structure, and of the 

 Source of Irritability. 



Note F.F. 



In the very lowest orders of animals a muscular structure does not exist in a distinct 

 state. Their partial movements are performed by means of the cellular tissue of wliich 

 they are composed. In the lowest of the series possessing- a muscular texture, it moves 

 only the integuments to which it is attachedj and of which it even forms a part. In all 

 animals possessed of a heart, the muscular tissues constitues an important part. In all 

 the vertebrated animals a small number only of the muscles are attached to the mucous 

 surfaces, to the skin and its appendages ; whilst the greatest proportion is connected 

 with the skeleton for the purposes of progression. 



According to the researches of Dr. Isenflamm, of Dorpat, into the progressive de- 

 velopment of the muscular structure in the human foetus, this tissue is formed from the 

 mucous and gelatinous fluid of which the embryo is at first composed; 



From this mucous fluid the involutary muscles are at first developed, and afterwards 

 the voluntary. During the first three months the voluntary muscles present the ap- 

 pearance of viscous layers, with a slight yellowish tint. At the end of the third month 

 the tendons make their appearance. During the fourth and fifth months the muscles 

 become redder, more fibrous, and more easily to be distinguished from their tendons. 

 In the sixth month, although very soft, they are still more perfect. At the full term 

 of utero-gestation the muscles are formed, but they are pale, yet vascular ; they are 

 soft, and their bulk much greater in proportion to the tendinous and aponeurotic sub- 

 stances than in the adult. 



As age advances, the voluntary muscles become redder and more fuUy developed, 

 and towards the decline of life, more rigid, less capable of quick and extensive contrac- 

 tion, and comparatively of less bulk than their aponeurotic and tendinous connexions. 



The microscopic observations of M. Bauer, Sir Everard Home, Messrs. Prevost, Du- 

 mas, and Beclard, seem to prove that the ultimate muscular fibre is composed of cor- 

 puscles (arranged like a string of beads) in every respect similar to those in the cen- 

 tre of the red globules of the blood. However, to obtain a correct idea of the ultimate 

 conformation of the muscular fibre, researches ought to be made with this view on the 

 raw and unprepared muscle : for the action of heat, of alcohol and acids, evidently 

 produces changes in the fibre, and coagulates the albumen, which enters into its com- 

 position. 



The voluntary nerves dip into the texture of the voluntary muscles at different points, 

 and divide into numerous minute fibrils, which abruptly escape demonstration. This 

 sudden manner of disappearing is owing to the extreme fibrils having become sol'. 

 and diaphanous, and deprived of their proper envelopes, so that their medullary sub- 

 stance is diffused, as it were, into the mucous tissue, connecting the muscular fibres. 



The cerebro-spinal nerves, although they are numerous and large in the voluntary 

 muscles, disappear in the manner just pointed out, long before their divisions be- 

 come sufficiently numerous to be distributed to each muscular fibre. This being the 

 case, how can the action of these nerves on all the fibres be explained ? They cannot 

 be the direct cause of the muscular contraction, but must act in producing it through 

 the medium of another and a more general conformation* What this formation appear.! 

 to us to be, we will now endeavour briefly to show. 



It has been stated that all the involuntary muscles are supplied with the ganglu-.l o: 

 soft nerves only ; that they surround the arteries throughout their ramifications, an ' 

 consequently are thus present in the voluntary muscles and in all vascular parts ; tl:a 

 the voluntary nerves themselves, whether we trace the process of their formation in the 

 human embryo, or observe them in the lower orders of animals, seem to originate from 

 the ganglial, the cerebro-spinal masses being the perfectien of the nervous conforma- 

 tion, and the last part of it which becomes completely developed, and that the cere- 

 bro-spinal nerves are destined to the performance of functions distinct from those to 

 which the other and more generally diffused class is alloted. As irritability is present 

 in parts which do not receive voluntary nerves, and in animals which do not possess 



this part of the nervous sytem, this property cannot be attributed to it. To wha't other 

 species of organization can we refer this property ? We find it, in the r 



the more perfect an!- 



