460 PROF. ST. GEORGE MITAET ON THE 



axial system, as do the epipleural spines of fishes, e. g. those so well developed in the 

 Herring. He appears to have considered the limb-girdles as hypertrophied radial 

 parts left after others primitively (or ideally) existing with them had disappeared. He 

 says they are formed " under the tegumentary covering, and therefore external to the 

 proper visceral wall of the body." The limbs of higher animals than fishes he regards a8 

 formed in the following way : — " By atrophy or otherwise, one or more of the segments 

 in the successive transverse rows of actinapophysial elements disappear, so as to leave in 

 Man one in the arm, two in the next row for the coracoid and clavicle, and one in the 

 proximal row for the scapula." He is " inclined to believe that the coracoid is an acti- 

 napophysial segment between the humerus and scapula, prolonged downwards towards 

 the haemal margin of the body ; that the scapula is a proximal element, elongated 

 towards the neural margin of the body ; that the clavicle is the only other retained 

 element in the same transverse row as the coracoid "^. 



In 1871 ^ Professor Humphrey, recalling to recollection the fact that the dorsal and 

 ventral rnid lines of the trunk are formed by the junction of the bifold lamince dorsales 

 and ventrales respectively, thence deduced the conclusion that the azygos fins of fishes 

 must be of bifold origin. He also puts forward the view that the pectoral and ventral 

 fins are but certain portions of the inferior azygos fins, which are separated (or, rather, 

 hindered from uniting) by the interposed body-cavity. Thus he regards the pelvic 

 bones of the ventral fins and the so-called " carpals " of the pectoral fins as modified 

 interspinous bones. 



In this way the limbs of higher animals would be (as Maclise had before represented 

 them to be) modified portions of the ventral azygos fin. 



In 1872, Professor Gegenbaur ' threw out the suggestion that the shoulder-girdle was 

 a modified arch of similar nature to the branchial arches (/. e. a part of the visceral 

 skeleton), and that the limbs may have been formed from tlie diverging rays of such 

 an arch. This view he has confirmed and supported in more recent publications in 

 1874* and 1876^. The azygos fins of fishes are considered by him to be parts seg- 

 mented off from the neural or hsmal spines of the vertebral column ''. 



In April, 1877, Professor Macalister, in treating ^ of the development of the muscular 

 system, and in a later publication ^ has spoken of vertebrate limbs in such a way as 



' L. c. p. 181. 



" Cambridge Journal of Anatomy and Physiologj-, vol. v. (seeond series, vol. iv.) page 58, plate ii. 



^ Untcrsuehungen, Heft 3, p. 181, note. 



■" Grundriss d. vergl. Anat. page 49-t. His words are, " Das ganze eiiiem Fiederblatte iihnliche Skelet- 

 geljilde stimmt aufi'allcnd mit manohen Stiitzapparaton der Selachier-Eiemen, und liisst dadurch ein Streif Licht 

 auf die Frage von der Pliylegenese der Gliedmassenbildungon fallen." 



^ ilorphologisches Jabrbuch, ii. Baud, drittes Heft, p. 417, fig. 4. 



" Grundriss der vcrgl. Anatomic, 1874, p. 488. 



' Dublin Medical Journal for April 1877. 



* Address to British Association of 1877, reported in ' Nature.' 



