442 
a certain number of myotomic buds (DoHRN) — the M. parietalis 
ventralis becomes divided into two portions, one lying anterior and 
the other posterior to the coracoid (procoracoid, GEGENBAUR). To that 
portion which lies between coracoid and lower jaw is commonly given 
the name “hypoglossus musculature”, because it forms the region of 
distribution of those anterior ventral spinal nerves (FRORIEP) which 
compose the hypoglossus (XII) nerve. While the hypoglossus muscu- 
lature loses in ontogeny its primitive connection with the myotomes 
from which it arose, the ventral half of the lateral musculature behind 
the procoracoid remains in contact with the dorsal, being separated 
merely, in the fishes for example, by a horizontal, connective tissue 
septum which stretches from the vertebral column to the skin, i. e. 
to the lateral line. The conditions are even simpler in Amphioxus 
and the Myxinoids, which possess no paired appendages, and in which 
the horizontal myoseptum is wanting. The latter is also true for 
Lepidosteus and Petromyzon in the region posterior to the gills. In 
Petromyzon the ventral musculature extends without interruption into 
the region beneath the gill openings forward to the mouth, while the 
dorsal (M. par. dorsalis) passes forward above the furrow in which 
the gill openings lie as far as the snout. 
HATscHER (92) has called attention to the fact, previously noted 
by WIEDERSHEIM (’80) and Juin (87), that the M. parietalis 
ventralis in the branchial region shows fewer segments than M. 
parietalis dorsalis, and he seeks to explain this discrepancy 
by supposing that the visceral clefts prevent the ventral growth of 
some of the myotomes and that in consequence these possess no ventral 
portions. HATSCHER’S results tend to throw no shadow of doubt upon 
the view that the ventral muscle of the branchial region is derived 
from myotomic buds and therefore the homologue of the muscle of 
this region (hypoglossus musculature) in Gnathostomata. Of its innerv- 
ation, HATSCHEK does not speak. 
On the other hand, the results of Kuprrer (95) lead us to 
question such homology. From the study of embryos of Petromyzon 
Planeri of 4—6 mm, he concludes that the “Bauchmuskel”!) of the 
branchial region is ectodermal in origin, arising in situ by the 
proliferation of cells from an ectodermal thickening which lies just 
ventral to the visceral pouches on each side of the embryo. Furthermore, 
1) Not to be confused with that muscle in Amphioxus to which 
J. Mitrer (’44) gave the name “Bauchmuskel”. 
