ANATOMY OF BALiENOPTERA ROSTRATA. 
• 207 
no synovial membranes intervened between them and the atlas. There were no condy- 
loid foramina. The calvarial portion was convex posteriorly towards the foramen mag- 
num, and was marked by an obscure central protuberance, from which very faintly 
marked ridges were traceable running forwards and outwards. More anteriorly a blunt 
median ridge existed, which was bounded on either side by a superficial concavity 
for muscular attachments. Its inner or cerebral surface was concave generally, but pre- 
sented a prominent median ridge, which was deeply grooved on the right side for the 
superior longitudinal sinus. 
The basioccipital portion of the bone projected forwards to meet the posterior border 
of the basisphenoid ; it was marked by a ridge on each side, where it articulated with 
the bullate tympanic bone; its inferior surface was also rough and concave, for the 
attachment of the anterior cervical muscles ; its cerebral surface was slightly concave in 
the antero-posterior direction, and presented a transverse ridge, where it united with 
the body of the sphenoid bone. 
Each exoccipital element extended outwards from the external border of the fora- 
men magnum and terminated by articulating with the mastoid or squamous bone ; it 
presented a rough surface posteriorly and inferiorly for muscular attachments, and was 
separated from the condyles behind by a deep notch, which formed the posterior boun- 
dary of the jugular foramen. 
The squamous bone was irregular in shape, and was composed of, first, a large, some- 
what crescentic glenoidal process, the inferior surface of which was concave, and formed 
a large but shallow cavity for the articulation of the lower jaw ; its anterior extremity 
was nearly in contact with the orbital plate of the frontal, and the posterior extended 
backwards on a level with the anterior border of the occipital condyles ; to this the sterno- 
mastoid and several other muscles were attached. A deep sulcus, perhaps the homologue 
of the digastric groove, existed internal and posterior to the process, giving origin to the 
depressor muscle of the lower jaw ; this sulcus ran backwards and outwards, and was 
separated from a second groove, which existed on its outer side for the reception of the 
posterior and external process of the periotic bone, by a sharp ridge which ran in the 
same direction ; the posterior border united with the lateral process of the occipital bone 
by an extensive surface, which extended as far as the posterior superior angle of the 
parietal. The lateral aspect of this process was convex in front and concave posteriorly 
and superiorly ; inwards or towards the temporal fossa it was deeply hollowed, where it 
was continuous in front and above with the squamous plate, from which it was sepa- 
rated below and anteriorly by a large fissure. 
The squamous plate was slightly convex, its temporal surface looked upwards and 
outwards; it was a narrow slip of bone and united anteriorly, by suture, with the 
posterior border of the parietal, and a small portion of the basisphenoid, which was here 
to be seen intermediate between the other bones forming the temporal fossa. Inferiorly 
and in front the squamous plate was continued into a pyramidal mass, which was 
directed forwards to meet the posterior border of the pterygoid bone, the outer edge 
of which it overlapped. The temporal surface was smooth, and its inferior aspect pre- 
