The Development of the Cartilaginous Skull ete. in Necturus. 437 
tive of the roofing cartilage than the topographically accurate tectum 
synoticum first suggested by Gaupp (’93). 
In Necturus of 46mm, the anterior part of the chorda still 
persists. but lies above the axial cartilage of the basal plate. The 
chorda enters the plate in the transverse plane passing through the 
posterior wall of the auditory capsule, and gradually, from the 
periphery inwards, becomes chondrified, while the tissue bounding 
the chorda is so modified that the chorda does not come into imme- 
diate contact with the cartilage of the basal plate, but passes through 
the axis of the plate to unite with the anterior prolongation of the 
first neural arch, thus forming the odontoid process (Tuberculum 
nterglenoidale of Gaupp) in the manner described by STÖHR 
for Triton. 
A summary of the facts presented in this part of the study is 
given at the close of the paper. 
Part. DIE 
The Muscles. 
It is the purpose of the third part of this study to show, chiefly 
by reference to the figures already described in demonstration of 
the development of the branchial cartilages, the origin and position 
of the tissue to which each of the chief muscles of the head, ex- 
cepting the eye-muscles, may be traced, and further to discuss the 
segmental relations of the hypoglossus musculature. 
I have connected the study of the development of the branchial 
muscles with that of the cartilages for two reasons; first, because 
v. Kuprrer ('95, page 119) claims that in Petromyzon cells of 
ectodermic origin similar to those which give rise to the branchial 
cartilages also take part in the formation of the ventral longitudinal 
muscle of the branchial region, and secondly because GORONOWITSCH 
(93, page 254) describes the »periaxiale Stränge«, which are partly 
composed of neural crest cells, as associated in the bird with the 
formation of the musculature of the visceral arches. 
In Necturus the mesectoderm cells do not take part in the 
formation of muscular tissue, but each muscle of the branchial region 
may be traced directly to tissue which is from the first distinctly 
mesodermic. Moreover, NEAL (97) has recently shown that the muscle 
thought by v. Kuprrer to be derived in Petromyzon from the 
ectoderm, actually arises by budding from the dorsal myotomes. 
