728 ALLIS. [Vor. XII. 
of the notochord, and it lies, in sections, approximately opposite 
the united vagus roots. Opposite the second segment, and 
distributed to that segment, lies the anterior occipital 
nerve ; opposite the third, the second nerve ; and opposite the 
fourth and fifth, the first and second occipital ganglia. No 
ventral root was found opposite to, or belonging to, the first 
muscle segment, nor could the innervation of that segment by 
branches of other roots be established. It seems, however, 
probable that it is innervated by branches of the first occipital 
nerve. 
In 20 mm. larvae the occipitale laterale has fused, at its 
upper end, with the hind end of the auditory capsule, and 
at its lower end, with the cartilaginous base of the skull. 
In certain vertical sections through it, it is seen to have two 
thin portions, with a third thin portion between it and the 
skull. It therefore presents three transverse enlargements. 
From the hind end of the first or anterior of these enlarge- 
ments the first intermuscular septum arises; from the hind 
end of the second, the second septum; and from the third, the 
third septum. The third enlargement is fused with, and forms 
part of, the enlarged hind end of the base of the skull. Pos- 
terior to that base, between it and the first separate cartilagi- 
nous, dorsal vertebral process, lies the first dorsal occipital 
arch, and other arches and processes follow regularly. The 
dorsal process between the two occipital arches is thus, at this 
age, not fused with the hind end of the cartilaginous base of 
the skull, and we have a vertebra or part of a vertebra in 
process of absorption. 
The vagus foramen in 20 mm. larvae is beginning to be en- 
closed by a cartilaginous process which forms between it and 
the first occipital nerve. In 25 mm. larvae it is entirely in- 
closed, and at 30 mm. the two first occipital nerves are also 
separated by a line of cartilage. The other arrangements and 
relations of the parts here under consideration are the same as 
at 20 mm., except that the trunk muscles already push forward 
somewhat into the temporal groove, and that a thick, tough 
line of tissue begins to be evident extending from the upper, 
hind edge of the skull backward into the first muscle segment. 

