142 JOHN BEARD. 
them are remains of the neural ridge. Still less can I accept 
Spencer’s recent suggestion,! that “the two curious branches 
which unite respectively the fifth and seventh and fifth and 
third cranial nerves” ... “may be regarded as persistent 
parts of the lateral nerve which united the ganglia of the sense 
organs along the lateral line in the head, and which, separa- 
ting from the skin, have come in the course of development to 
occupy a much deeper position, together with the ganglia, with 
which they preserve their primitive connection.” 
These “curious branches” are portions of fused supra- 
branchial nerves, as a glance at the diagrams (figs. 46 and 51) 
will show. 
THe ReEwations or THE Heap anp TRUNK IN 
VERTEBRATES. 
Many attempts have been made to homologise the compo- 
nents of the segments of the head and trunk, and naturally 
such attempts have extended to the nerves. The spinal nerves, 
it is hardly necessary to say, present an anterior and posterior 
root, and the posterior one is ganglionated. Such a state of 
affairs has been sought for also in the head, but in face of the 
facts previously recorded it is at least doubtful, even if the 
evidence of cranial anterior and posterior roots be granted, 
whether these can be homologised with those of the spinal nerves. 
The posterior roots of cranial and spinal nerves develop differ- 
ently, for the spinal have no connection with the skin in early 
stages; that is, the ganglion is never fused with the skin, and 
their roots are never connected with gill-clefts or with special 
sense organs. 
One of the most striking results of these researches is the 
great distinction of the body of Vertebrates into a gill-bearing 
region, and a non-gill-bearing region; and at present, with 
the sharply-defined differences which obtain in the develop- 
ment of the organs of these two regions, attempts to homologise 
organs in the two different regions would seem to meet with indif- 
1 Spencer, ‘ Notes on the Early Development of Rana temporaria,’ 
p- 12. 
