NL. 
Squalus acanthias | Petromyzon marinus 
pin 
as 
Somite or Myotome < = '5 |Somite or Myotome eae Ventral Nerve-root 
5a 
M. rectus posterior !) 3 |M. rectus posterior 2 VI 
Degenerates 4 |Degenerates VII None 
1st post-otic, Degenerates 5 |1st post-otic Myo. IX 
in early stages. 
2nd post-otic. Degene- 6 |2nd a as x 1st to 5th post-otie 
rates in late stages. myotomes innervated 
3nd post-otic. 1st perma- 7 |3rd nn 35 x by the ventral roots 
nent myotome. of the 4th—5th post- 
¢ , ’ 7 2 
sh post: otic 8 oe an 35 ae otic myotomes ‘) 
myotomes give rise 9 - ” 2} Bi 
10 [6th 53 ” 2nd ,, 3rd sp 
by buds to hypo- #7 th 3rd Ath 
glossus musculature ae A giveriseby en h 2% 
12 oth buds to the AEB 3 oat te 
The 13th and following} 13* M = ‘ramus re- 
myotomes give rise by *9th :@Bar= HH), 6th ,, eurrens vagi” 
buds to the appendi-| 14* |*10th vent. bran- 6th theese of KUPFFER. 
cular and ventral mus-| 15* [*11th a 7th N Sth „ 
eulature (behind the, 16 12 8th ,, 9th ,, 
procoracoid) | 
parietalis ventralis lies three segments posterior to that (4th 
post-otic) wich in Squalus forms. the anterior segment of the hypo- 
glossus musculature. We may draw from this the interesting con- 
clusion that in these two forms, buds from myotomes three segments 
removed come to lie in the same relative position anterior to the 
hyoid arch. The evidence that we possess shows, however, that this 
anterior segment does not enter into the formation of the muscles of 
the tongue (‘‘piston lingual”) of Petromyzon, as it does in Gnatho- 
stomata. Busor (91, p. 82) states that at metamorphosis “les muscles 
du piston lingual et ceux du pharynx naissent dans le tissu embryon- 
naire apparu apres la déstruction du velum et de la glande thyroide”. 
While I am not satisfied that the evidence given by Busor has 
excluded the possibility that the M. par. ventralis contributes to 
the formation of the muscles of the “piston lingual”, especially as he 
states in agreement with ScHNEIDER (79) that this muscle is wanting 
in the branchial region of Ammocoetes, I nevertheless consider it 
highly probable that the so-called tongue of Petromyzon is not the 
1) No mention of the nature, number or homologies of segments 
anterior to the rectus posterior myomere is made in this paper. 
2) The Hypoglossus autorum. Those segments are starred (*) below 
which are found the pronephric tubules, 
Anat, Anz. XIII. Aufsätze, 30 
