14:0 The Development of the Arm in Man 



are drawn from these models, and are to be consulted in connection with 

 the descriptions given in this article. Dr. Mall's embryos are stained in 

 alum caraiine or alum cochineal. 



PART I. 



Relation of the Myotomes to the Arm Bud. 



literature. 



Considerable study and perhaps even more theorizing has been done 

 on the relation of the myotomes to the musculature of the limbs. The 

 present state of our knowledge upon this subject is far from satisfactory, 

 especially in the higher vertebrates. The great difficulty or impossi- 

 bility in many cases of distinguishing between the cells at the ventral 

 edge of the myotomes and those in the neighboring portion of the limb 

 bud renders the problem very difficult. Experimental work, such as 

 has been done by Byrnes,^ may lead to a clear understanding of the 

 relations in the lower vertebrates. The majority of workers appear to 

 have been able to trace myotomic processes into the limbs. Mollier ■* 

 has shown in Selachians that myotome buds enter into the fin anlage or 

 pectoral plate. From these buds are developed the muscles. From the 

 mesoderm between the buds are developed the fin rays. Braus " also 

 shows myotome buds going into the pelvic fins of Selachians. Dohrn * 

 finds two buds from each myotome, an anterior and a posterior, entering 

 the fin anlage, these he believes form the fin muscles. Balfour^ holds 

 that the limb muscles in Elasmobranchii come from muscle plate buds. 

 Harrison * has shown that in teleosts the pectoral fins are derived wholly 

 from the somatopleure and that the myotomes take no part in the 



3 Byrnes, Experimental studies on the development of the limb muscles in Am- 

 phibia, Jour, of Morph., Vol. XIV, 1898. 



''Mollier, Zur Entwickelune: der Selachierextremitaten, Anat. Anz., Vol. VII, 

 1893, p. .3.51. Die paarigen Extremitaten der Wirbelthiere, Anal Hefte, Bd. Ill, 

 1893. 



5 Braus, Beitrage zur Entwi-ckeluno; der Muskulatur und des peripheren Nerven- 

 system der Selachier, Morph. Jahr., Bd. XXVII, 1899, p. .501. 



6 Dohrn, Studien zur Urgeschichte des Wirbelthier Korpers, VI, etc., Mittheil. aus 

 der Zool. Station zu Neapel, Bd. V, 1884. 



1 Balfour, Comp. Emb., 3nd. Ed., 1885. 



8 Harrison, Die Entwickelung d. unpaaren und paaren Flosseu der Teleostier, 

 Archiv f. Mikr. Anat., Bd. XLVI, Ileft 3, 1895. 



