200 ALUS. [Vol. XVIII. 



The dorsal surface of the anterior portion of the superior divis- 

 ion of the g-eniohyoideus Hes immediately underneath the mucus 

 membrane that lines the mouth cavity, and the united muscles of 

 opposite sides of the head here form that part of the floor of the 

 mouth cavity that lies in front of and under the tongue. The 

 tongue lies in the V-shaped space formed between the dorsal sur- 

 faces of the united muscles, and nearly fills the anterior end of the 

 mouth cavity, its pointed, anterior end extending almost to the 

 apex of the mandible. The thin membrane that connects the 

 hyoid apparatus with the mandible, and thus completes the floor 

 of the mouth cavity, extends from the ventral edge of the man- 

 dible to the dorso-lateral edge of the anterior portion of the 

 superior division of the geniohyoideus, and, posterior to that 

 muscle, to the external surface of the ceratohyal, somewhat lateral 

 to the middle line of the bone. This membrane is formed, as in 

 Amia, by the fused external dermis and internal lining membrane 

 of the mouth, and it is in it, near its attachment to the ceratohyal, 

 that the small, tendinous head of the superior geniohyoideus has 

 its origin. 



The Hyghygideus can be considered,*in Scomber, as in Amia, 

 as having two divisions, a superior and an inferior one, but the 

 inferior division arises in part from the second instead of entirely 

 from the first, or most anterior, branchiostegal ray. This inferior 

 division of the muscle has two distinct portions, each of which 

 is usually partly double. One of these portions lies partly 

 superficial to, or ventral to, the other portion, and it is 

 much more independent of the superior division of the muscle, 

 and much less a continuation of that muscle, than the deeper 

 portion is. It arises mainly from the anterior edge of the 

 most anterior branchiostegal ray, but there is a posterior con- 

 tinuation of the muscle in fibers that lie between the most 

 anterior and the next posterior ray. The line of origin of the 

 muscle begins some little distance from the base of the associated 

 ray and extends distally to its free end. The muscle usually arises 

 in two somewhat separate portions, which run mesially and for- 

 ward, and, uniting, have a single, broad, flat tendon, which crosses 

 the middle line of the head and is inserted on the ventral surface 

 of the hypohyal of the opposite side. The muscle of the left side 



