ABR 
homologue of the tongue of higher Vertebrates. This conclusion is 
based on the following grounds. 1) The anterior segment of the M. 
parietalis ventralis remains the same in its relation in Petro- 
myzon as in Ammocoetes, i. e. without relation to a tongue. 2) While 
the muscles of the tongue of higher Vertebrates are derived from the 
anterior segment of the M. parietalis ventralis, which lies 
anterior to the hyoid arch, in Petromyzon the muscles of the “piston 
lingual” extend throughout the length of the branchial region and 
terminate posteriorly in the cartilaginous pericardium. They are quite 
separate from the M. parietalis ventralis which lies lateral and 
ventral to them 1). 
It has been stated by several investigators (Born, ’27; SCHLEMM 
u. D’ALTON, ’38; An Born ’84; and Junin, ’87) that the muscles of 
the pharynx and “piston lingual” are innervated by branches of the 
vacus (or glossopharyngeus) after anastomosis of this nerve with the 
anterior ventral spinal nerve roots to which have been given the name 
hypoglossus (XI). Kuprrer (96) has, however, shown that in Ammo- 
coetes these anterior spinal ventral nerve roots innervate the anterior 
myotomes of the M. parietalis dorsalis and not musculature 
ventral to the furrow in which the gill openings lie. In spite of the 
greatest pains I have been unable to detect an anastomosis of the two 
anteriormost ventral spinal nerves with either the glossopharyngeus 
or the vagus, and I must state that it is my conclusion on the basis 
of this and other evidence stated above that spinal ventral roots do 
not innervate the musculature of the tongue of Petromyzon. 
While the five myotomes which in Squalus form the hypoglossus 
musculature lie as a group anterior to those five myotomes which in 
Petromyzon form the anterior portion of the M. par. ventralis, the 
results are different when we compare those segments which in these 
two forms contain the pronephros. The number of pronephric tubules 
in Petromyzon embryos of the day of hatching varies from 4 to 5, 
the first of these, however, lying always below the 7th post-otic myo- 
tome. In Squalus embryos of 42—43 post-otic somites, the Anlage 
of the pronephros consists of segmental outpocketings of the somato- 
1) I have stated this evidence of the difference in the relations of 
the tongue of Petromyzon and Gnathostomata lest one not familiar with 
these relations should think that an organ of the same name in these 
Vertebrates should therefore be an homologous organ. As a matter of 
fact, no comparative anatomist has attempted to homologize these two 
kinds" of, tongues. See Wocr and June (’87), WIEDERSHEIM (’93) and 
GEGENBAUR (’94). 
