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102 The American Naturalist. [February, 
branchial arches, the other that of the vertebral arteries ; the one 
of the branchiomeres, the other of the myotomes. The existing 
branchiomeres do not appear to be secondary to the myotomes, 
but secondary to primary hypothetical branchiomeres. In the 
hyoid and mandibular arches, and in the region of the head- 
cavity supplied with the III. nerve, are to be assumed a greater 
number of primitive branchial clefts. Hyoid and spiracular clefts 
are to be considered as multiples of branchial clefts. The irregu- 
larity seen in the posterior branchial arches is connected with the 
changes that have caused the coalescing of branchial arches. 
Thyroid, mouth, hypophysis, and nose are evidently related to 
the branchial system. Gegenbaur holds that the branchial skele- 
ton is secondarily derived from ribs. But the ribs are dorso- 
lateral structures, and the branchial arches ventral. If the latter 
are secondary articulations of the vertebral column, then traces of 
the apophyses should be found. But as this does not occut, 
the branchial skeleton is to be regarded as of independent origin. 
The hyoid and mandibular cartilages then represent multiples, 
and cartilaginous girdles, which have functioned as branchial 
arches, now enter into the composition of the skull. 
LITERATURE. 
goa. Dourn, A. Bemerkungen über den neuesten Versuch yor 
Lösung des Wirbeltierkopf-Problems. Amat. Anz., V., Nos. 2 and e adi 
‘900. DOHRN, A. Studien zur Urgeschichte des Wirbelthierkörpers- 
XV. Neue Grundlage zur Beurteilung der Metamerie des Kopfs. Mittheil. 
Zool. Station, Neapel, IX., Heft 3, 1890. ER 
'89. HOFFMANN, C.K. Ueber die Metamerie des Nachhirns und Hinter 
hirns, und ihre Beziehung zu den segmentalen Kopfnerven bei Ree 
. HorrMann. In Bronn’$ Klassen und Ordnungen 2 = i 
Reichs. Bd. VI., Abth. IIL, pp. 1907-1914, 1938-2000, 1888-'89- 
bryos. Anat. Anz. IIl., p. 445, 1888. 
’89. RABL, C. Theorie des Mesoderms. Morph. Jahrbuch, >r ar 
2, 1889. 
88. KASTSCHENKO, N. Zur Entwickelungsgeschichte des Selachierem — 
, . bei 
89. VON OSTROUMOFF, A. Ueber die Froriep’schen ganglien Y 
Selachiern. Zool. Anz., No. 311, 1885. 
(To be continued.) 
