Dec, 13, 1 



NATURE 



J51 



sesamoids, as they are retrograded skeletal parts, which 

 in most cases have been preserved by the surrounding 

 muscles. (2) Arthrogenous sesamoids, like the os humero- 

 scapulare, are derived from the capsule of a joint. (3) 

 Tenontogenous or desmogenous, like the patella, are formed 

 heteroblastically inside of a tendon. 



The eighth and ninth chapters (pp. 894-947), form a 

 critical essay on muscles with regard to their connection 

 with the nervous system. After having exhaustively 

 criticized the neuro-muscle theory of Kleinenberg, the 

 various views of Iluxley, those of the brothers Hertwig 

 with reference to the coulom theory, and, lastly, the theory 

 of the secondp.ry connection of muscle- and nerve-fibres 

 as promulgated by Claus and Chun, the author coiisiders 

 the ontogeny, degeneration, and regeneration of muscles 

 and nerves. Lastly, he proceeds to attempt a decision 

 (pp. 920-41). 



In connection with this attempt stands a discussion of 

 the inheritance of acquired faculties, and the continuity 

 of germinal and somatic plasma. Fuerbringer believes in 

 Haeckel's law of accumulative adaptation through in- 

 heritance. What the individual has acquired during and 

 through its incessant contact with the world can greatly 

 influence its descendants ; hence the great importance 

 of the investigation of post-embryonic developmental 

 changes. Throughout the whole book, Fuerbringer, with- 

 out denying the importance of the ontogenetic features as 

 a recapitulation of the ancestral history, lays more stress 

 upon the study and comparison of the adult forms. In 

 almost every chapter, we come across instances in which 

 the embryonic development does not help to explain 

 certain organs ; the recapitulation of their previous 

 stages is too much hurried or condensed, and at the best 

 only that is repeated which had last been acquired. 



Fuerbringer accepts Kleinenberg's neuro-muscle theory 

 as the most probable solution. The whole apparatus, 

 which consists of a ganglionic cell, a nervous and a 

 muscular fibre, has been developed from one and the same 

 cell, and is therefore to be looked upon as one organ. 

 The muscle is the end-organ of its nerve, consequently the 

 innervation of the muscles forms the most trustworthy 

 means for the determination of their homologies. 



Chapter x. (pp. 947-72) deals with the variability of 

 muscles. Neither the point of the origin, nor that of 

 the insertion, of muscles is a safe guide to their homologies. 

 This shows why muscles are almost valueless for the 

 determination of the homologies of skeletal parts. 



Pp. 972 91, on the shifting or migration of the ex- 

 tremities with their girdles along the vertebral axis. This 

 shifting has reached its highest degree in birds. Even 

 individual and one-sided variations are frequent. As a 

 rule, the shifting has been directed backwards, resulting 

 in an increase of the length of the neck. Large birds 

 show a greater amount of shifting than the smaller ones 

 of the same family. A retrograde or secondary shifting 

 towards the head seems to stand in correlation with the 

 degradation of the wings. Hand in hand with the changes 

 of the relative position of the limb and girdle goes a 

 change of the whole thorax. Thoracic vertebrae are turned 

 into cervical, and lumbar into thoracic vertebra;. In most 

 cases, but not always, the number of thoracic ribs remains 

 the same. It looks as if, roughly speaking, the whole trunk 

 with all the organs inclosed in it, did slide along the 

 vertebral axis. The accompanying metamerical trans- 

 formation of the plexus brachialis is not effected by inter- 

 or excalation of nervous segments, but by the diminution 

 and reduction of ons anterior nerve-stem, and the con- 

 temporary formation and addition of a nerve nearer to 

 the posterior end of the plexus. The peripheral parts of 

 the plexus retain their configuration in spite of all the 

 changes, and since the only trustworthy safeguard in the 

 homologies of spinal nerves is their number in the series 

 of metameres, two plexuses may be homodynamous, 

 although, strictly speaking, not homologous. This is 



expressed by the term "imitatory homodynamy," more 

 happily by " parhomology." 



The same considerations apply to the muscles. They, 

 together with the nerves, undergo metameric changes 

 until they likewise are only parhomologous. The various 

 muscles of the shoulder-girdle of a bird with thirteen 

 cervical vertebra; may present, in shape, position, and 

 distribution of the nerves, features identical with those of a 

 bird with fifteen cervical vertebra;, but still they are only 

 parhomologous to each other. 



This metameric transformation cannot, of course, be 

 watched on those muscles which arise from the shoulder- 

 girdle, but on those which, like the mm. rhomboidales et 

 serrati, arise from the trunk, and are insetted into the 

 girdle. The migration of the whole anterior extremity 

 tailwards necessitates first elongation, then a thinning out, 

 and even total reduction, of those muscles which extended 

 from the neck to the anterior end of the shoulder-girdle. 

 In this way the m. hvator scapulae of the reptiles has 

 become lost by the birds. 



Of course the whole problem of the metameric trans- 

 formation and new formation of muscles and nerves 

 cannot be considered as solved without an explanation of 

 the histological changes which are involved in the ques- 

 tion of the parhomology of the muscles together with their 

 nerves. Such an explanation Fuerbringer has not been 

 able to present, but he tries to suggest one by showing 

 how we may imagine those changes to take place. 



Most muscles, P"uerbringer argues, are polymeta- 

 meric, i.e. they receive nervous fibres from two or more 

 spinal roots. Moreover, the nerves of the more proximal 

 muscles belong chiefly to the pre-axial or anterior, whilst 

 those of the distal or more peripheral muscles receive their 

 nerves mostly from the post-axial roots of the plexus. The 

 author discards the idea that nerve fibres can send out 

 buddings into neighbouring new muscles, but thinks that 

 in many cases the formation of new muscles and nerve- 

 fibres is initiated by a splitting. This splitting begins 

 peripherally with the muscle-fibre, is followed by that of 

 the nerve-fibre, and perhaps leads to a division of the 

 ganglionic cell. Ganglionic cells with two axial cylinders 

 of motory nerves are known to occur. 



Another possible explanation of the increase of the 

 number of fibres of one nerve and those of one muscle is 

 their derivation from cells which had remained latent in 

 an embryonic or primordial condition between the fully 

 formed muscle- and nerve-cells. Traces of such prim- 

 ordial elements Fuerbringer has found between the fibres 

 of motory nerves, and between the fibres of fully developed 

 muscles ; in the latter case they may be identical with the 

 myoblasts of other authors. 



Everywhere in nature, in the organism, there is super- 

 fluity of material. Tissues and organs seem to be trained 

 by the struggle for existence in such a way that they 

 produce at their beginning an abundance of formative 

 germs and cells, of which under ordinary circumstances 

 only a small part becomes developed into specifically 

 functional tissue cells. The rest remain in their primi- 

 tive embryonic condition. They form stored-up plastic 

 material, which may or may not be called upon to meet 

 such extraordinary requirements as may arise from the 

 necessity for the organism to adapt itself to new 

 conditions. 



.Still greater is the difficulty when the neomorphism (by 

 which word the reviewer has on a previous occasion tried 

 to render into English the meaning of the German term 

 " Neulnidting,^' — new formation not being exactly identical 

 with it) is not confined to the same, but takes place in the 

 next following metamere. For instance, when a muscle, 

 which previously was innervated by the fibres from the 

 15th and 16th spinal nerves, now receives its supply from 

 the 15th, i6th, and 17th nerves, the explanation given 

 above will be of no avail. The permanent continuity of 

 the two later components of the original neuro-muscle 



