164 



ANNELIDA. 



it were, the excretory ducts leading from the 

 interior, and conducting out the sanious and 

 sabulous matter which proceed from the dege- 

 nerated cartilages, synovial membranes, and 

 bones of the diseased joint. The skin is thin, 

 soft, and shining, and moveable on the sur- 

 face, except where the fistulous orifices exist. 



The anatomical characters of this disease in 

 its advanced stage affecting this articulation we 

 have many opportunities of observing. When 

 the superficial coverings of the swelling are 

 removed, the fat is remarked to be consistent 

 and yellow, the cellular tissue interposed be- 

 tween the ligaments, tendons, and muscles is 

 infiltrated with a viscid, semi-fluid, spongy, 

 homogeneous mass ; sometimes this tissue be- 

 comes so thick, and is so connected with the 

 lateral ligaments of the ankle-joint, and so in- 

 terposed among their softened fibres, as to render 

 a clean dissection of these last impracticable ; so 

 that the ligamentous and cellular structures 

 around the joint appear to have undergone a 

 species of fibro-cartilaginous degeneration ; the 

 viscid glairy matter infiltrated around the joint 

 with the tumefied ligaments are the parts which 

 cause the principal swelling, and give to the fingers 

 examining it that deceptive feeling of fluctuation 

 which characterises the white swelling wherever 

 situated. 



The few muscular fibres to be found near this 

 joint are pale and of a gelatinous appearance, 

 being infiltrated with the same matter as that 

 which pervades the more superficial structures. 

 The tendons, nevertheless, preserve their natural 

 colour and consistence. The periosteum will 

 be found much thickened and easily detached 

 from the bone. 



The bones of the joint, and those in its vici- 

 nity, are very usually more or less atrophied, 

 and have undergone a process of degeneration ; 

 notwithstanding, however, what has been said 

 on high authority to the contrary, these bones 

 are occasionally enlarged and expanded ; they 

 have lost much of their specific gravity, their 

 spongy tissue is softened, yellowish, and easily 

 penetrated by a knife, and filled with a matter 

 resembling a.dipocere, or a yellow semi-fluid 

 fat. 



The heel it has been noticed is elongated, 

 and the foot measured from the tibia to the 

 toes on the dorsum is shortened very generally, 

 and pointed downwards. Dissection discovers 

 the cause of this frequent phenomenon in a par- 

 tial dislocation of the tibia forwards on the 

 astragalus, the softened ligaments allowing the 

 action of the gastrocnemii and solaei to drag 

 the whole foot backwards. In the interior of 

 the articulation, a more or less considerable 

 quantity of a sanious matter is found ; while 

 the cartilages covering the end of the tibia 

 and fibula, and surfaces of the astragalus, are 

 softened, adhere but slightly to the bones, and 

 have been partially removed, leaving exposed 

 the porous structure of the latter. 



The arteries, veins, and capillaries present no 

 peculiarity, except that the naturally white 

 ligamentous tissue is more freely supplied than 

 usual with red vessels. The neurilema of the 

 posterior tibial nerve is evidently much thick- 



ened, so as to give it an appearance of enlarge- 

 ment; the small nerves around the joint seem 

 also hypertrophied. 



( R. Adams.) 



ANNELIDA, (a generally adopted, but 

 barbarous latinization of the French term 

 < Anne 1 ides,' from ' Annellus/ a little ring; 

 ought rather to be written * Annulata'or ' An- 

 nellata.') The natural group of Annelida 

 comprehends all the invertebrated animals 

 which have a soft body divided into transverse 

 segments or rings; a distinct central nervous 

 system disposed in the form of a longitudinal 

 gangliated chord, blood coloured (generally 

 red), and contained in a system of appropriate 

 and very distinct vessels ; and, lastly, organs of 

 locomotion, consisting either of fleshy appen- 

 dages provided with bristles, or of bristles only ; 

 or of a prehensile cavity situated at each ex- 

 tremity of the body ; but never of articulated 

 members, as in the Arachnida, Crustacea, and 

 Insecta. 



The establishment of this class is due to 

 Cuvier. Prior to him, Pallas, Miiller, and 

 Otho Fabricius, had made observations of great 

 interest on the animals of which it is com- 

 posed; and we find in the writings of the 

 author of the Miscellanea Zoologica the most 

 happy ideas respecting the natural relations 

 which these animals bear to one another. 

 Nevertheless, these works had at first but little 

 influence on the classification of the Inverte- 

 brata, and for a long time naturalists persisted in 

 following the method of Linnaeus, who united 

 under the term Vermes,the Mollusca, Zoophyta, 

 and Annelida, and dispersed the latter in three 

 different sections of that great class ; confound- 

 ing some with the Entozoa (intestinal worms), 

 others with the Acephalous Mollusca, and others 

 again with the Testacea. 



It was in the work entitled " Tableau Ele- 

 mentaire de THistoire Naturelle des Animaux," 

 published in the years 1797-8, that M. Cuvier 

 laid the first foundation of a natural distribution 

 of invertebrated animals. He collected together 

 in the class Vermes the species which more lately 

 have constituted the groups of Annelida and 

 Entozoa, and established in it the two divisions 

 corresponding to those which are generally 

 adopted at the present day. Having subse- 

 quently determined the presence of red blood 

 in the leech, and having investigated the circu- 

 lating apparatus in these animals, Cuvier sepa- 

 rated the " red-blooded'' from the " intestinal" 

 worms, and constituted for the former a distinct 

 class, to which Lamarck afterwards gave the 

 name of " Annelides," which has been gene- 

 rally adopted, and is used at the present day 

 by most naturalists.* 



This classification being based essentially on 

 anatomical structure, has been adopted by 

 Lamarck, Dumeril, Savigny, Leach, Latreille, 



* See Cuvier, Bulletin des Sciences par la Societe 

 Philomathiqup, an vii. et x. Lamarck, Discours 

 d'ouverture du cours des Animaux sans Vertebres 

 prononce en Mai 1806, et Histoire des Animaux san* 

 Vertebres. 



