No. 3.] MUSCLES AND NERVES IN AMIA CALVA. 753 
selachians. In Acipenser and in teleosts he describes them, 
calling them, in the latter, the obliqui ventrales. In Amia 
these muscles resemble, in a general way, the dorsal inter- 
arcual muscles ; that is, there is on each arch an interarcual 
ligament, a muscle that has its insertion on its own arch, and 
another that tends to have its insertion on the next posterior 
arch. They therefore probably arise from the ventral portion 
of the interbranchiale of Chimaera, as Vetter concludes, but 
they belong, with that muscle, to the deeper layer of the 
primitive constrictor, and not to the superficial layer. 
The pharyngo-claviculares externus and internus are probably 
the obliqui muscles of the fifth arch. 
40. The geniohyoideus and intermandibularis arise together. 
The geniohyoideus has an inferior and a superior portion. 
From, or in connection with, the anterior end of the inferior 
portion, the intermandibularis arises. The latter muscle is 
double, both parts extending from mandible to mandible. The 
superior division of the geniohyoideus extends from mandible 
to hyoid, and seems to be one of the obliqui ventrales of the 
mandibular arch. The inferior division occupies a position 
intermediate between that of the superior division and that of 
the intermandibularis, and may also be an obliquus ventralis, 
or more probably the interbranchial muscle of the arch, in 
which case the intermandibularis probably belongs to the same 
muscles. 
41. The hyohyoideus, in its superior portion, is the inter- 
branchial muscle of its arch. In its inferior portion it may be 
partly the obliquus ventralis. 
42. The branchiomandibularis is found in Acipenser and 
Polypterus as well as in Amia. It is represented in Elasmo- 
branchii by the coraco-mandibularis, or by part of that muscle. 
In teleosts it is not found. In Amia it varies greatly in dif- 
ferent individuals, and undoubtedly represents a muscle in 
process of deterioration and disappearance. It is probably, as 
McMurrich has suggested, a muscle from which the muscles of 
the tongue, in higher vertebrates, have developed. It is inner- 
vated by a terminal branch of the united first, second, and 
third occipital nerves. 
