458 MR. ST. GEORGE MIVART ON THE [June 24, 
backwards, it is inserted into the outside of the dorsal part of the 
first branchial arch, immediately beneath the insertion of the second 
part of the digastric. 
Deepest muscles of left side of ventral surface of head, the cerato-hyotdeus 
externus being drawn strongly forwards. 
(.A.1, @. A. 2, & C.A.3. Constrictores arcuum. C. H. £2. Cerato-hyoideus ex- 
ternus. C H.J. Cerato-hyoideus internus. M.H.1 & M.H.2. Mylo- 
hyoideus. S. H. Sterno-hyoid. 
Cerato-hyoideus internus* (fig. 5, C. H.I). A very much smaller 
muscle than the last, and, as Fischer says, “spindle-shaped and ten- 
dinous at each end.” It arises from the inner end of the posterior 
surface of the hyoidean cornu, and is inserted into the lower end of 
the dorsal segment of the first branchial arch. 
Constrictores arcuumt (fig. 5, C.A.1, C. A. 2, and C. 4. 3). 
There are three of these small muscles. The first connects the 
ventral end of the second branchial arch with the dorsal end of the 
ventral segment of the first branchial arch. The second and largest 
of the three connects together the ventral ends of the dorsal segments 
of the first and third branchial arches. The third muscle connects 
together the ventral ends of the dorsal segments of the second and 
third branchial arches. 
A musclef (figs. 4 & 5, S. H), which corresponds to the sterno- 
hyoideus of Menopoma, though here there is no sternum, and is in 
fact the anterior continuation of the rectus, passes forwards and is 
inserted into the dorsal surface of the urohyal and into the ventral 
surface of the ventral segment of each first branchial arch, near its 
junction with the basihyal. 
* Fischer, l. c. p. 72, tab. i. fig. 4, pa. 
+ Fischer, 7. c. p. 74, tab. 1. fig. 38, ca and ca’. 
} Fischer, /.c. p. 104. 
