43 
Triceratops was identified by Lull as part of the origin area of the com- 
plexus or longissimus dorsi. This muscle, however, usually lies beneath, 
and lateral to, the cranial segment of the capiti-dorsi-clavicularis. An 
elongate attachment area like the one in Triceratops particularly suggests 
a sheet-like muscle, which is the usual form of the capiti-dorsi-clavicularis. 
In Chasmosaui'us (Figure 7, cdc .) , how- 
ever, the corresponding area is sub-circular 
in shape, and is confined to the basal por- 
tion of the parietal. In Styracosaurus, 
Centrosaurus, and Anchiceratops the area 
is poorly defined, but seems to extend con- 
siderably back along the median line of 
the crest, as in Triceratops, The insertion 
of this muscle, in the absence of a clavicle, 
was probably on the anterodorsal angle of 
the scapula. 
Biventor cervicis (spino-occipitalis). 
On the skull of Chasmosaurus there is an 
ovoid depression (Figure 7, b.c.) just above 
the foramen magnum, and below the at- 
tachment pit of the capiti-dorsi-clavicu- 
laris. The writer identifies this as the 
common insertion area of the biventor 
cerivicis muscles. The corresponding area 
is single in Centrosaurus and Anchicera- 
tops, paired in Styracosaurus and Triceratops. Lull included these pits in 
the attachment area of the “complexus”. 
Longissimus cervico-capitis (complexus?) . On the Chasmosaurus skull 
there are two ovoid areas situated on the parietal and exoccipital lateral to 
the biventor cervicis pit. The upper of these two depressions (Figure 7, 
Lee.) may be assigned to the longissimus cervico-capitis muscle, one branch 
of the longissimus dorsi. In Styracosaurus , Centrosaurus, and Anchicera- 
tops the two depressions are more or less subtrigonal in shape, and lie along 
the dorsal margin of the paroccipital process. Triceratops has a single, 
ovoid excavation in this region. 
Rectus capitis posticus major. To this muscle the writer assigns the 
lower or inner one (Figure 7, r.c.p.m.) of the two depressions mentioned 
above. In Triceratops there appears to have been a common insertion 
with the longissimus cervico-capitis. 
Rectus capitis anticus minor. A shallow depression (Figure 7, r.c.a.m .) 
in the lower distal angle of the exoccipital in Chas?nosaurus probably repre- 
sents the insertion area of this muscle. The area is not well defined in 
other forms examined. 
Two other muscle attachments were noted by Lull in Triceratops. 
There is a small ovoid one well up on the parietal, near the squamosal 
suture. This was assigned with question to the levator scapulee. It seems 
much more probable, however, that this muscle had its normal origin from 
the anterior cervicals. The writer is unable to suggest the identity of the 
attachment in question. Lull also noted the large area on the squamosal 
Figure 7. Chasmosaurus belli 
(Lanibe), plesiotype, Geol. 
Surv., Canada, No. 2280, pos- 
terior view of occipital re- 
gion, showing muscle attach- 
ments: be., biventor cervicus; 
cdc., capiti-dorsi-clavicularis ; 
l.c.c., longissimus eervico-capi- 
tis; pm?, parieto-mandibul- 
aris?; r.c.a.m., rectus capitis 
anticus minor; r.c.p.m., rec- 
tus capitis posticus major; 
■v i 
3312—8 
